feat(inventory): implement inter-project material transfer backend

- Add ProjectTransfer database model and migration
- Implement project transfer service with immediate stock deduction on creation
- Support 100% full delivery receipt logic across destination warehouses
- Enforce canonical_specs_hash matching for cross-project stock merge
- Add RBAC guards and status lock on received transfers (409 Conflict)
- Register API router for transfers with on-the-way integration

backend/app/main.py

@@ -31,6 +31,7 @@ from app.db.init_db import (
     ensure_dashboard_tables,
     ensure_material_topic_column,
     ensure_quote_projects,
+    ensure_project_transfers_table,
     ensure_v26,
 )
 from app.observability import RequestContextMiddleware, setup_logging
@@ -107,6 +108,7 @@ async def lifespan(_app: FastAPI):
     await ensure_v26(engine)
     await ensure_audit_table(engine)
     await ensure_drop_category_tables(engine)
+    await ensure_project_transfers_table(engine)
     task = asyncio.create_task(_auto_expire_loop()) if settings.AUTO_EXPIRE_ENABLED else None
     try:
         yield