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.

scripts/test-web-search-candidate.mjs

@@ -0,0 +1,59 @@
+import assert from "node:assert/strict";
+
+import { probeMcp, rpc } from "../docker/web-search/mcp-probe.mjs";
+
+const url = process.argv[2];
+if (!url) throw new Error("usage: node scripts/test-web-search-candidate.mjs <mcp-url>");
+
+await probeMcp(url, { timeoutMs: 10_000 });
+
+function payload(result) {
+  const text = (result.content || []).find(part => part.type === "text")?.text;
+  return text ? JSON.parse(text) : result.structuredContent;
+}
+
+const search = payload(await rpc(url, 3, "tools/call", {
+  name: "search_web",
+  arguments: { q: "candidate diagnostic fixture", limit: 3, provider: "searxng" }
+}, 30_000));
+assert.equal(search.items[0].title, "Deterministic Search Result");
+assert.equal(search.providerUsed, "searxng");
+assert.equal(search.diagnostics.attempts[0].status, "success");
+assert.equal(search.diagnostics.attempts[0].result_count, 1);
+
+const httpFetch = payload(await rpc(url, 4, "tools/call", {
+  name: "fetch_url",
+  arguments: { url: "http://mock-search.test:8080/dynamic", engine: "http", format: "text" }
+}, 30_000));
+assert(!httpFetch.content.includes("BROWSER_RENDERED_MARKER"));
+
+const browserFetch = payload(await rpc(url, 5, "tools/call", {
+  name: "fetch_url",
+  arguments: { url: "http://mock-search.test:8080/dynamic", engine: "browser", format: "text", timeout_ms: 20_000 }
+}, 60_000));
+assert(browserFetch.content.includes("BROWSER_RENDERED_MARKER"));
+
+const blocked = await rpc(url, 6, "tools/call", {
+  name: "fetch_url",
+  arguments: { url: "http://127.0.0.1:8765/private", engine: "browser" }
+}, 30_000);
+assert.equal(blocked.isError, true);
+assert((blocked.content || []).some(part => part.text?.includes("Blocked localhost/private URL")));
+
+const blockedRedirect = await rpc(url, 7, "tools/call", {
+  name: "fetch_url",
+  arguments: { url: "http://mock-search.test:8080/redirect-private", engine: "browser" }
+}, 30_000);
+assert.equal(blockedRedirect.isError, true);
+
+await rpc(url, 8, "tools/call", {
+  name: "fetch_url",
+  arguments: { url: "http://mock-search.test:8080/websocket-attempt", engine: "browser", fresh: true }
+}, 30_000);
+const websocketCount = payload(await rpc(url, 9, "tools/call", {
+  name: "fetch_url",
+  arguments: { url: "http://mock-search.test:8080/ws-count", engine: "http", format: "text", fresh: true }
+}, 30_000));
+assert.equal(websocketCount.content.trim(), "0");
+
+console.log("pass web-search candidate diagnostics, browser rendering, and SSRF rejection");