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-lock.json

@@ -15,6 +15,7 @@
         "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",
@@ -7264,6 +7265,12 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/minisearch": {
+      "version": "7.2.0",
+      "resolved": "https://registry.npmjs.org/minisearch/-/minisearch-7.2.0.tgz",
+      "integrity": "sha512-dqT2XBYUOZOiC5t2HRnwADjhNS2cecp9u+TJRiJ1Qp/f5qjkeT5APcGPjHw+bz89Ms8Jp+cG4AlE+QZ/QnDglg==",
+      "license": "MIT"
+    },
     "node_modules/morgan": {
       "version": "1.10.1",
       "resolved": "https://registry.npmjs.org/morgan/-/morgan-1.10.1.tgz",