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/docs/constraints.txt

@@ -10,7 +10,6 @@ build==1.5.0
 certifi==2026.6.17
 cffi==2.0.0
 charset-normalizer==3.4.7
-chromadb==1.5.9
 click==8.4.2
 cryptography==49.0.0
 durationpy==0.10
@@ -35,7 +34,6 @@ joblib==1.5.3
 jsonschema==4.26.0
 jsonschema-specifications==2025.9.1
 kubernetes==36.0.2
-llms-txt-mcp==0.2.0
 markdown-it-py==4.2.0
 MarkupSafe==3.0.3
 mcp==1.28.0