P0-fix: plugin migrations use migration engine (crm_migration) instead of API engine (crm_api)

- main.py: registry.initialize(get_migration_engine()) instead of get_engine()
- main.py: plugin migrations run via get_migration_session_factory() not async_session()
- registry.py: upgrade_plugin, install_plugin, uninstall_plugin all use migration session for DDL
- db/__init__.py: get_migration_engine() raises RuntimeError if MIGRATION_DATABASE_URL missing (no fallback)
- Fixes fresh-install failure: crm_api has no DDL rights, plugin migrations need crm_migration

app/main.py

@@ -154,7 +154,8 @@ async def lifespan(app: FastAPI):
 
     # Initialize plugin registry and discover built-in plugins
     registry = get_registry()
-    registry.initialize(get_engine(), app)
+    from app.core.db import get_migration_engine
+    registry.initialize(get_migration_engine(), app)
     registry.discover_builtins()
 
     # Install discovered builtin plugins and activate only those marked active in DB
@@ -201,12 +202,16 @@ async def lifespan(app: FastAPI):
                 await db.flush()
                 logger.info(f"Created plugin record: {name} (core={plugin.manifest.is_core})")
 
-            # Run migrations if not yet applied
+            # Run migrations if not yet applied — use MIGRATION engine (crm_migration) for DDL
             if plugin.manifest.migrations:
                 try:
-                    await registry.migration_runner.run_all_migrations(
-                        db, name, plugin.manifest.migrations
-                    )
+                    from app.core.db import get_migration_session_factory
+                    mig_session_factory = get_migration_session_factory()
+                    async with mig_session_factory() as mig_db:
+                        await registry.migration_runner.run_all_migrations(
+                            mig_db, name, plugin.manifest.migrations
+                        )
+                        await mig_db.commit()
                 except Exception as exc:
                     logger.error(f"Migration FAILED for {name}: {exc}")
                     if plugin_record.active: