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/searxng.js

@@ -0,0 +1,47 @@
+import { HTTP_TIMEOUT, SEARXNG_URL } from "../constants.js";
+import { fetchWithTimeout } from "../utils/http.js";
+import { getRandomUserAgent, getAcceptLanguageHeader } from "../utils/user-agent.js";
+import { searchCache, createCacheKey } from "../utils/cache.js";
+
+export class SearXNGProvider {
+  name = "searxng";
+
+  constructor(instanceUrl) {
+    this.instanceUrl = instanceUrl || SEARXNG_URL;
+  }
+
+  async search(q, limit, lang, signal) {
+    const cacheKey = createCacheKey("searxng", q, limit, lang);
+    const cached = searchCache.get(cacheKey);
+    if (cached) return cached;
+    const params = new URLSearchParams({ q, format: "json", language: lang, safesearch: "0" });
+    const response = await fetchWithTimeout(`${this.instanceUrl}/search?${params}`, {
+      headers: { "User-Agent": getRandomUserAgent(), ...getAcceptLanguageHeader(lang) },
+      signal
+    }, HTTP_TIMEOUT);
+    if (!response.ok) {
+      if (response.status === 403) throw new Error("SearXNG JSON API disabled");
+      throw new Error(`SearXNG error: ${response.status}`);
+    }
+    const data = await response.json();
+    const items = (data.results || []).slice(0, limit).map(result => ({
+      title: result.title || "",
+      url: result.url || "",
+      snippet: result.content || undefined,
+      source: "searxng"
+    }));
+    searchCache.set(cacheKey, items);
+    return items;
+  }
+
+  async isAvailable() {
+    try {
+      const response = await fetchWithTimeout(`${this.instanceUrl}/search?q=test&format=json`, {
+        headers: { Accept: "application/json", "User-Agent": getRandomUserAgent() }
+      }, 5000);
+      return response.ok;
+    } catch {
+      return false;
+    }
+  }
+}