MCP: make the namespace truthful

[fredporter]

Outcome

• leaves udos_mcp as the sole implementation under backend/app/mcp
• moves Feed activity storage and TOON context caching to app/services without changing their APIs
• removes unused HiveMind server/launcher, consensus engine, second LLM router, Roundtable integration, and duplicate knowledge layer
• removes false port-8490 health, recovery, menu, HUD, watchdog, service registry, and cost-routing claims
• keeps the canonical agent registry, Flow Router, budget API, uKnowledge routes, and official MCP gateway as the single owners
• aligns active Feed, Plates, Spool, and Developer chat specs

Contraction

• 1,895 lines removed; 40 lines added

Verification

• 412 backend tests passed
• 12 frontend tests passed and production build passed
• 3 udos-mcp protocol tests passed
• changed-file Ruff, docs, governance, route audit, namespace assertion, and diff checks passed