Overhaul docs retrieval and web search quality

Replace the abandoned llms-txt-mcp/Chroma docs backend with an in-repo
MCP service: SQLite WAL + FTS5 + sentence-transformer embeddings,
transactional source replacement, persisted state across restarts,
singleflight refresh with conditional requests, hybrid lexical/semantic
ranking with exact-duplicate collapse, source/host filters, and
explicit-by-default content retrieval. Add docs_rebuild and a
docs-rebuild CLI command.

Add deterministic llms-full.txt snapshot generation for machine-local
menus with hash-validated provenance manifests; lifecycle commands
promote a local menu to its snapshot only when the manifest validates.
Switch public source profiles to content-bearing llms-full.txt feeds.

Improve web search: bounded provider fallback with per-attempt
diagnostics and cancellation, an optional Brave Search API provider,
strict SearXNG engine selection, capped link/media extraction, and a
real engine=browser renderer that routes every request through the
existing SSRF vetting while blocking WebSockets, non-GET traffic, and
private destinations.

Extend release checks with offline unit suites and isolated candidate
container tests for both images.

docker/web-search/overrides/bing.js

@@ -43,7 +43,7 @@ export class BingProvider {
     }
   }
 
-  async search(q, limit, lang) {
+  async search(q, limit, lang, signal) {
     const cacheKey = createCacheKey("bing", q, limit, lang);
     const cached = searchCache.get(cacheKey);
     if (cached)
@@ -51,7 +51,10 @@ export class BingProvider {
     const market = getMarketFromLang(lang);
     const results = await browserPool.withBrowser(async (browser) => {
       const page = await browser.newPage();
+      const abort = () => void page.close().catch(() => undefined);
+      signal?.addEventListener("abort", abort, { once: true });
       try {
+        signal?.throwIfAborted();
         await page.setViewport({ width: 1365, height: 768 });
         await page.setUserAgent(DEFAULT_BROWSER_SEARCH_USER_AGENT);
         await page.setExtraHTTPHeaders(getAcceptLanguageHeader(lang));
@@ -95,7 +98,8 @@ export class BingProvider {
         });
       }
       finally {
-        await page.close();
+        signal?.removeEventListener("abort", abort);
+        if (!page.isClosed()) await page.close();
       }
     });
     searchCache.set(cacheKey, results);