ai: migrate docs-search to @crema/lexical-rag-ui

Replace the in-app docs-search.ts and build-docs-index.mjs with the
new sibling lib (@crema/lexical-rag-ui). Wire-up only — same index
shape, same tool response shape, same MiniSearch config, so the agent
sees no behavior change.

- tsconfig + app.css: wire the lib; alias minisearch to consumer's
  node_modules so sibling-lib resolution works.
- admin-tools.ts: createRAGClient("/docs-index.json"), keep search_docs
  tool's response shape unchanged (collapse tags[] back to category).
- ai.tsx: define DocHit locally — it's the tool-response shape, no
  longer the lib's internal type.
- scripts/build-docs-index.mjs: thin wrapper that injects MiniSearch
  and calls buildIndex. Per-app sources list and tags live here.
- package.json: add minisearch dep + build:docs script + prebuild hook.
- .gitignore: don't commit the generated /public/docs-index.json.

Delete: app/lib/docs-search.ts (was untracked; its logic moved to lib).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -3,13 +3,15 @@
   "private": true,
   "type": "module",
   "scripts": {
+    "prebuild": "npm run build:docs",
     "build": "react-router build",
     "dev": "react-router dev",
     "start": "react-router-serve ./build/server/index.js",
     "typecheck": "react-router typegen && tsc",
     "test": "vitest run",
     "test:watch": "vitest",
-    "sync-libs": "node scripts/sync-libs.mjs"
+    "sync-libs": "node scripts/sync-libs.mjs",
+    "build:docs": "node scripts/build-docs-index.mjs"
   },
   "dependencies": {
     "@base-ui/react": "^1.4.0",
@@ -21,6 +23,7 @@
     "d3-geo": "^3.1.1",
     "isbot": "^5.1.36",
     "lucide-react": "^1.8.0",
+    "minisearch": "^7.2.0",
     "motion": "^12.38.0",
     "openapi-fetch": "^0.17.0",
     "phoenix": "^1.8.5",