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/bounds.mjs

@@ -0,0 +1,23 @@
+const MAX_LINKS = 500;
+const MAX_IMAGES = 200;
+const MAX_VIDEO = 50;
+const MAX_AUDIO = 50;
+const MAX_ATTACHMENTS = 10;
+
+export function boundFetchCollections(result) {
+  const warnings = [...(result.warnings || [])];
+  const trim = (value, maximum, label) => {
+    if (!Array.isArray(value)) return value;
+    if (value.length > maximum) warnings.push(`${label} truncated from ${value.length} to ${maximum}`);
+    return value.slice(0, maximum);
+  };
+  if (result.links) result.links = trim(result.links, MAX_LINKS, "links");
+  if (result.media) {
+    result.media.images = trim(result.media.images, MAX_IMAGES, "images");
+    result.media.videos = trim(result.media.videos, MAX_VIDEO, "videos");
+    result.media.audio = trim(result.media.audio, MAX_AUDIO, "audio");
+  }
+  if (result.attachments) result.attachments = trim(result.attachments, MAX_ATTACHMENTS, "attachments");
+  result.warnings = warnings;
+  return result;
+}