feat: implement three-tier module classification and framework layer

Module Classification:
- Core (4): core, tenancy, cms, customers - always enabled
- Optional (7): payments, billing, inventory, orders, marketplace, analytics, messaging
- Internal (2): dev-tools, monitoring - admin-only

Key Changes:
- Rename platform-admin module to tenancy
- Promote CMS and Customers to core modules
- Create new payments module (gateway abstractions)
- Add billing→payments and orders→payments dependencies
- Mark dev-tools and monitoring as internal modules

New Infrastructure:
- app/modules/events.py: Module event bus (ENABLED, DISABLED, STARTUP, SHUTDOWN)
- app/modules/migrations.py: Module-specific migration discovery
- app/core/observability.py: Health checks, Prometheus metrics, Sentry integration

Enhanced ModuleDefinition:
- version, is_internal, permissions
- config_schema, default_config
- migrations_path
- Lifecycle hooks: on_enable, on_disable, on_startup, health_check

New Registry Functions:
- get_optional_module_codes(), get_internal_module_codes()
- is_core_module(), is_internal_module()
- get_modules_by_tier(), get_module_tier()

Migrations:
- zc*: Rename platform-admin to tenancy
- zd*: Ensure CMS and Customers enabled for all platforms

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

alembic/env.py

@@ -213,6 +213,41 @@ if config.config_file_name is not None:
 target_metadata = Base.metadata
 
 
+# ============================================================================
+# MODULE MIGRATIONS DISCOVERY
+# ============================================================================
+# Discover migration paths from self-contained modules.
+# Each module can have its own migrations/ directory.
+# ============================================================================
+
+def get_version_locations() -> list[str]:
+    """
+    Get all version locations including module migrations.
+
+    Returns:
+        List of paths to migration version directories
+    """
+    try:
+        from app.modules.migrations import get_all_migration_paths
+
+        paths = get_all_migration_paths()
+        locations = [str(p) for p in paths if p.exists()]
+
+        if len(locations) > 1:
+            print(f"[ALEMBIC] Found {len(locations)} migration locations:")
+            for loc in locations:
+                print(f"  - {loc}")
+
+        return locations
+    except ImportError:
+        # Fallback if module migrations not available
+        return ["alembic/versions"]
+
+
+# Get version locations for multi-directory support
+version_locations = get_version_locations()
+
+
 def run_migrations_offline() -> None:
     """
     Run migrations in 'offline' mode.
@@ -229,6 +264,7 @@ def run_migrations_offline() -> None:
         target_metadata=target_metadata,
         literal_binds=True,
         dialect_opts={"paramstyle": "named"},
+        version_locations=version_locations,
     )
 
     with context.begin_transaction():
@@ -249,7 +285,11 @@ def run_migrations_online() -> None:
     )
 
     with connectable.connect() as connection:
-        context.configure(connection=connection, target_metadata=target_metadata)
+        context.configure(
+            connection=connection,
+            target_metadata=target_metadata,
+            version_locations=version_locations,
+        )
 
         with context.begin_transaction():
             context.run_migrations()