feat(pi-web-search): 统一 web_search/web_fetch 并由主模型路由搜索厂商

7 个按厂商命名的搜索工具收敛为 2 个统一工具，schema 与提示词不再暴露
provider 概念：web_search 由当前主模型按内置规则在 Tavily/Exa/Keenable
间路由（会话内 LRU 缓存，失败按可用性降级），web_fetch 固定走 Exa 并
静默降级。三家均改为纯 fetch 直连——Exa 直接对 mcp.exa.ai 发 JSON-RPC
并缓存会话，彻底移除 pi-mcp-adapter、@tavily/pi-extension 与
@keenable/pi-search 依赖。

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

package.json

@@ -26,6 +26,7 @@
     "pi-tool-search/CHANGELOG.md",
     "pi-tool-search/LICENSE",
     "pi-tool-search/UPSTREAM.md",
+    "pi-web-search",
     "pi-worktree",
     "pi-permission-system/LICENSES",
     "pi-permission-system/docs/auto-review",
@@ -50,9 +51,7 @@
     "extensions": [
       "./extensions/search-config.ts",
       "./extensions/fff-override.ts",
-      "./extensions/tavily-override.ts",
-      "./node_modules/@keenable/pi-search/src/index.ts",
-      "./extensions/mcp.ts",
+      "./pi-web-search/index.ts",
       "./extensions/codegraph.ts",
       "./pi-rtk-optimizer/index.ts",
       "./extensions/hashline.ts",
@@ -73,17 +72,14 @@
       "./pi-tool-search/extensions/index.ts"
     ],
     "skills": [
-      "./node_modules/context-mode/skills",
-      "./node_modules/@keenable/pi-search/skills"
+      "./node_modules/context-mode/skills"
     ]
   },
   "dependencies": {
     "@ff-labs/pi-fff": "0.10.5",
     "@gotgenes/pi-permission-system": "file:./pi-permission-system",
-    "@keenable/pi-search": "0.1.2",
     "@ogulcancelik/pi-minimal-footer": "file:./pi-minimal-footer",
     "@smoose/pi-notify": "file:./pi-notify",
-    "@tavily/pi-extension": "0.1.2",
     "context-mode": "1.0.169",
     "jiti": "2.7.0",
     "pi-ask-user": "file:./pi-ask-user",
@@ -92,9 +88,9 @@
     "pi-hashline-edit": "0.8.3",
     "pi-hermes-memory": "file:./pi-hermes-memory",
     "pi-lsp": "0.1.7",
-    "pi-mcp-adapter": "2.26.0",
     "pi-ssh": "file:./pi-ssh",
     "pi-tool-search": "file:./pi-tool-search",
+    "pi-web-search": "file:./pi-web-search",
     "pi-worktree": "file:./pi-worktree",
     "ssh2": "1.17.0",
     "typescript": "6.0.3",