feat: 移除 Codex Fast mode 与 AutoReview 后台分析，模型改为配置驱动

移除 pi-extension-codex-fast-mode：
- 删除整个扩展目录；同步清理根 package.json 的 files / pi.extensions /
  dependencies 条目、package-lock.json、tests/extension-load.test.ts 断言
  与文档章节。
- pi-minimal-footer 的 Fast on 渲染是该扩展的唯一消费者。扩展移除后 accent
  分支不再有生产者，collectFooterStatusItems 简化为直接返回非空状态字符串，
  去掉 FooterStatusItem 与 accent 标志，避免留下死代码。

移除 500 次裁决后的后台分析体系：
- 删除 analysis-agent.ts（192 行）与 ledger.ts（296 行），以及对应的
  auto-review-runtime / auto-review-ledger 测试。
- runtime.ts 由 177 行收敛到 85 行：安装选项缩为 { service, config }；删除
  handleAgentSettled 与 agent_settled 注册；保留 session_start / turn_start
  （denial circuit breaker 属安全语义）/ session_shutdown。
- 删除 analysis 配置键：config、extension-config、config-schema、生成的
  permissions.schema.json 与种子配置。
- 删除 reviewer 的 onDecision 回调（唯一消费者是 ledger）。
- 删除迁移机制 scripts/migrate-permission-policy.mjs、其测试与 update.sh 中
  46 行 migrate_permission_policy 接线。种子部署保持“目标缺失才写入”，已存在
  的 policy.jsonc 永不被覆盖。

AutoReview 模型改为纯配置驱动：
- 删除 DEFAULT_PROVIDER / DEFAULT_MODEL 常量与 findCodexTemplate 合成逻辑；
  model.ts 由 65 行收敛到 48 行。
- provider / model 任一缺失时返回新增失败类别 model-unconfigured 并 defer 到
  人工审批；provider 未注册或模型未发布同样 defer。
- reasoning 不再有默认常量，完全由配置决定。
- session_start 在 auto-review 已列入 authorizerChain 且 provider/model 未配齐
  时 ui.notify 提示一次，避免不使用 AutoReview 的用户被打扰。
- 种子 autoReview 只保留 enabled，provider/model/reasoning 由用户按本机实际
  可用的模型填写。

破坏性变更：analysis 键已从 strictObject schema 删除，任何仍带该键的
policy.jsonc 会使整份配置被拒（fail-closed 到全 ask）。这是刻意的变更，已由
config-loader 测试固定，防止将来无声放宽。

测试：
- 新增 auto-review-model.test.ts（7 例），覆盖此前完全缺失的模型解析：真实
  命中、未配置、provider 未知、模型未发布，以及不再合成替代模型。
- 重写 auto-review-runtime.test.ts（6 例）：authorizer 注册、未配置时提示
  一次、已配置 / disabled / 无 UI / 不在 chain 时静默。
- config-loader.test.ts 新增 2 例：带 analysis 的旧配置被拒且 fail-closed、
  autoReview 逐字段合并。
- composition-root.test.ts 的 EXPECTED_HANDLERS 移除 agent_settled。

文档：AGENTS.md、README.md、pi-permission-system 的 README / CHANGELOG /
configuration.md / architecture.md / auto-review UPSTREAM.md。

验证：pi-permission-system 的 typecheck、2577 个测试与 build 全部通过；根 50
个测试通过；schema 重新生成无漂移；新种子通过 schema 校验；5 个脚本 sh -n
通过；git diff --check 无空白问题。未安装 shellcheck；未执行真实 pi install /
update（属外部写操作）。

scripts/migrate-permission-policy.mjs

@@ -1,236 +0,0 @@
-#!/usr/bin/env node
-
-import { createHash } from "node:crypto";
-import { constants } from "node:fs";
-import {
-  chmod,
-  open,
-  readFile,
-  rename,
-  unlink,
-} from "node:fs/promises";
-import { basename, dirname, join } from "node:path";
-import { fileURLToPath } from "node:url";
-
-/** Semantic hash of the previously installed personal policy snapshot. */
-export const LEGACY_PERMISSION_POLICY_HASHES = new Set([
-  "9abf020e80fceae8c52de3e8b758822dfc86cb90e9083381e2569dde1e29400a",
-]);
-
-function stripJsonComments(text) {
-  let output = "";
-  let inString = false;
-  let escaped = false;
-  let lineComment = false;
-  let blockComment = false;
-
-  for (let index = 0; index < text.length; index += 1) {
-    const character = text[index];
-    const next = text[index + 1];
-    if (lineComment) {
-      if (character === "\n") {
-        lineComment = false;
-        output += character;
-      }
-      continue;
-    }
-    if (blockComment) {
-      if (character === "*" && next === "/") {
-        blockComment = false;
-        index += 1;
-      }
-      continue;
-    }
-    if (inString) {
-      output += character;
-      if (escaped) escaped = false;
-      else if (character === "\\") escaped = true;
-      else if (character === '"') inString = false;
-      continue;
-    }
-    if (character === '"') {
-      inString = true;
-      output += character;
-    } else if (character === "/" && next === "/") {
-      lineComment = true;
-      index += 1;
-    } else if (character === "/" && next === "*") {
-      blockComment = true;
-      index += 1;
-    } else {
-      output += character;
-    }
-  }
-  return output;
-}
-
-function stripTrailingCommas(text) {
-  let output = "";
-  let inString = false;
-  let escaped = false;
-  for (let index = 0; index < text.length; index += 1) {
-    const character = text[index];
-    if (inString) {
-      output += character;
-      if (escaped) escaped = false;
-      else if (character === "\\") escaped = true;
-      else if (character === '"') inString = false;
-      continue;
-    }
-    if (character === '"') {
-      inString = true;
-      output += character;
-      continue;
-    }
-    if (character === ",") {
-      let lookahead = index + 1;
-      while (/\s/.test(text[lookahead] ?? "")) lookahead += 1;
-      if (text[lookahead] === "}" || text[lookahead] === "]") continue;
-    }
-    output += character;
-  }
-  return output;
-}
-
-export function parseJsonc(text, label = "policy.jsonc") {
-  try {
-    return JSON.parse(stripTrailingCommas(stripJsonComments(text)));
-  } catch (error) {
-    throw new Error(`${label} is invalid JSONC: ${error instanceof Error ? error.message : String(error)}`);
-  }
-}
-
-function sortJson(value) {
-  if (Array.isArray(value)) return value.map(sortJson);
-  if (value !== null && typeof value === "object") {
-    return Object.fromEntries(
-      Object.keys(value)
-        .sort()
-        .map((key) => [key, sortJson(value[key])]),
-    );
-  }
-  return value;
-}
-
-export function permissionPolicySemanticHash(text) {
-  const parsed = parseJsonc(text);
-  const canonical = JSON.stringify(sortJson(parsed));
-  return createHash("sha256").update(canonical).digest("hex");
-}
-
-function backupTimestamp(now) {
-  return now.toISOString().replace(/[:.]/g, "-");
-}
-
-async function readFileSnapshot(path) {
-  const noFollow = constants.O_NOFOLLOW ?? 0;
-  const handle = await open(path, constants.O_RDONLY | noFollow);
-  try {
-    const info = await handle.stat();
-    if (!info.isFile()) throw new Error(`policy path is not a regular file: ${path}`);
-    return { content: await handle.readFile("utf8"), dev: info.dev, ino: info.ino };
-  } finally {
-    await handle.close();
-  }
-}
-
-async function writeExclusive(path, content) {
-  const handle = await open(
-    path,
-    constants.O_WRONLY | constants.O_CREAT | constants.O_EXCL,
-    0o600,
-  );
-  try {
-    await handle.writeFile(content, "utf8");
-    await handle.sync();
-  } finally {
-    await handle.close();
-  }
-  await chmod(path, 0o600);
-}
-
-export async function migratePermissionPolicy(
-  policyPath,
-  seedPath,
-  options = {},
-) {
-  const now = options.now ?? new Date();
-  const legacyHashes = new Set(
-    options.legacyHashes ?? LEGACY_PERMISSION_POLICY_HASHES,
-  );
-  let original;
-  try {
-    original = await readFileSnapshot(policyPath);
-  } catch (error) {
-    if (error?.code === "ENOENT") return { status: "missing" };
-    throw error;
-  }
-
-  const seedContent = await readFile(seedPath, "utf8");
-  parseJsonc(seedContent, "bundled permission policy seed");
-  const currentHash = permissionPolicySemanticHash(original.content);
-  const seedHash = permissionPolicySemanticHash(seedContent);
-  if (currentHash === seedHash) {
-    await chmod(policyPath, 0o600);
-    return { status: "current" };
-  }
-  if (!legacyHashes.has(currentHash)) return { status: "custom" };
-
-  const backupPath = `${policyPath}.bak.${backupTimestamp(now)}`;
-  const temporaryPath = join(
-    dirname(policyPath),
-    `.${basename(policyPath)}.tmp.${process.pid}.${backupTimestamp(now)}`,
-  );
-  await writeExclusive(backupPath, original.content);
-
-  let temporaryCreated = false;
-  try {
-    await writeExclusive(temporaryPath, seedContent);
-    temporaryCreated = true;
-    if (options.beforeCommit) await options.beforeCommit();
-    const current = await readFileSnapshot(policyPath);
-    if (
-      current.dev !== original.dev ||
-      current.ino !== original.ino ||
-      current.content !== original.content
-    ) {
-      throw new Error(
-        "permission policy changed during migration; original file was preserved",
-      );
-    }
-    await rename(temporaryPath, policyPath);
-    temporaryCreated = false;
-    await chmod(policyPath, 0o600);
-    return { status: "migrated", backupPath };
-  } finally {
-    if (temporaryCreated) await unlink(temporaryPath).catch(() => undefined);
-  }
-}
-
-async function main() {
-  const [policyPath, seedPath] = process.argv.slice(2);
-  if (!policyPath || !seedPath) {
-    console.error(
-      "usage: migrate-permission-policy.mjs <policy.jsonc> <bundled-seed.jsonc>",
-    );
-    process.exitCode = 2;
-    return;
-  }
-  try {
-    const result = await migratePermissionPolicy(policyPath, seedPath);
-    console.log(
-      result.status === "migrated"
-        ? `migrated:${result.backupPath}`
-        : result.status,
-    );
-  } catch (error) {
-    console.error(error instanceof Error ? error.message : String(error));
-    process.exitCode = 1;
-  }
-}
-
-function isMainModule() {
-  return process.argv[1] && fileURLToPath(import.meta.url) === process.argv[1];
-}
-
-if (isMainModule()) await main();