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>

app/lib/admin-tools.ts

@@ -15,9 +15,13 @@ import {
   suspendTenant,
   type Tenant,
 } from "~/lib/arcadia/tenants"
-import { searchDocs } from "~/lib/docs-search"
+import { createRAGClient } from "@crema/lexical-rag-ui"
 import { BLOCK_INDEX, getBlockSchema } from "~/lib/block-schemas"
 
+// Lazy singleton — first tool call fetches /docs-index.json, subsequent
+// calls reuse the parsed MiniSearch instance.
+const docsClient = createRAGClient("/docs-index.json")
+
 export type ToolCall = {
   name: string
   args: Record<string, unknown>
@@ -253,8 +257,22 @@ const TOOLS: ToolDef[] = [
         10,
         Math.max(1, typeof args.limit === "number" ? args.limit : 5),
       )
-      const hits = await searchDocs(query, limit)
-      return { query, count: hits.length, hits }
+      const hits = await docsClient.search(query, { limit })
+      // Tool-shape parity with the previous searchDocs() return: collapse
+      // tags[] back to category for now so the agent's prior expectations
+      // and any cached examples still parse cleanly.
+      return {
+        query,
+        count: hits.length,
+        hits: hits.map((h) => ({
+          id: h.id,
+          title: h.title,
+          sourcePath: h.sourcePath,
+          category: h.tags[0] ?? "",
+          excerpt: h.excerpt,
+          score: h.score,
+        })),
+      }
     },
   },
   {