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>

observability/__init__.py

@@ -0,0 +1,73 @@
+"""
+Observability Module
+====================
+Provides metrics, tracing, and logging for the agent governance system.
+
+Components:
+- metrics: Prometheus-format metrics endpoint
+- tracing: Distributed tracing with spans
+- logging: Structured JSON logging with trace correlation
+"""
+
+from .metrics import (
+    registry,
+    router as metrics_router,
+    record_agent_execution,
+    record_violation,
+    record_promotion,
+    record_orchestration,
+    record_template_download,
+    MetricsMiddleware
+)
+
+from .tracing import (
+    Tracer,
+    Span,
+    Trace,
+    get_tracer,
+    get_current_trace_id,
+    get_current_span,
+    router as tracing_router,
+    TRACE_ID_HEADER,
+    SPAN_ID_HEADER,
+    extract_trace_context,
+    inject_trace_context
+)
+
+from .logging import (
+    get_logger,
+    StructuredLogger,
+    LogStorage,
+    router as logging_router
+)
+
+__all__ = [
+    # Metrics
+    'registry',
+    'metrics_router',
+    'record_agent_execution',
+    'record_violation',
+    'record_promotion',
+    'record_orchestration',
+    'record_template_download',
+    'MetricsMiddleware',
+
+    # Tracing
+    'Tracer',
+    'Span',
+    'Trace',
+    'get_tracer',
+    'get_current_trace_id',
+    'get_current_span',
+    'tracing_router',
+    'TRACE_ID_HEADER',
+    'SPAN_ID_HEADER',
+    'extract_trace_context',
+    'inject_trace_context',
+
+    # Logging
+    'get_logger',
+    'StructuredLogger',
+    'LogStorage',
+    'logging_router'
+]