BR-1: Register SIN-Brain memory tools in sin serve

[Delqhi]

Plan: docs/plans/bundle-memory-tools-integration.md

Register recall/remember/forget/pin/link_evidence as MCP tools in sin serve; surface sin-brain in sin status. Each behind try/except ImportError (graceful degradation).

Acceptance:

• Tools listed by a local MCP client
• sin status shows sin-brain (present/absent)
• Missing sin-brain does not crash serve
  Depends on: SIN-Brain SB-3.