Add Phase 10-12 implementation: multi-tenant, marketplace, observability

Major additions:
- marketplace/: Agent template registry with FTS5 search, ratings, versioning
- observability/: Prometheus metrics, distributed tracing, structured logging
- ledger/migrations/: Database migration scripts for multi-tenant support
- tests/governance/: 15 new test files for phases 6-12 (295 total tests)
- bin/validate-phases: Full 12-phase validation script

New features:
- Multi-tenant support with tenant isolation and quota enforcement
- Agent marketplace with semantic versioning and search
- Observability with metrics, tracing, and log correlation
- Tier-1 agent bootstrap scripts

Updated components:
- ledger/api.py: Extended API for tenants, marketplace, observability
- ledger/schema.sql: Added tenant, project, marketplace tables
- testing/framework.ts: Enhanced test framework
- checkpoint/checkpoint.py: Improved checkpoint management

Archived:
- External integrations (Slack/GitHub/PagerDuty) moved to .archive/
- Old checkpoint files cleaned up

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

checkpoint/STATUS.md

@@ -2,7 +2,7 @@
 
 ## Current Phase
 
-** NOT STARTED**
+** COMPLETE**
 
 ## Tasks
 
@@ -26,7 +26,7 @@
 - **Details**: Phase updated to complete
 
 ### 2026-01-23 23:25:09 UTC
-- **Phase**: NOT STARTED
+- **Phase**: COMPLETE
 - **Action**: Initialized
 - **Details**: Status tracking initialized for this directory.