feat(memory): add WritePipeline and MemoryService facade

Introduce a layered pipeline architecture for the memory write flow:
- WritePipeline: orchestrates preprocess → extract → store → cluster → summarize
  with deadlock retry, resource cleanup, and pilot-run support
- MemoryService: facade that delegates to WritePipeline, placeholder methods
  for read/forget/reflect
- BearLogger: structured step-level logging with perf threshold alerts
- Shadow pipeline integration in MemoryAgentService (env-gated pilot run)

Also includes:
- Fix deprecated SQLAlchemy declarative_base import
- Extend Neo4j Entity fulltext index to cover description and aliases
- Migrate Pydantic schemas to v2 (ConfigDict, field_validator)

api/app/repositories/neo4j/create_indexes.py

@@ -17,10 +17,9 @@ async def create_fulltext_indexes():
         #     CREATE FULLTEXT INDEX dialoguesFulltext IF NOT EXISTS FOR (d:Dialogue) ON EACH [d.content]
         #     OPTIONS { indexConfig: { `fulltext.analyzer`: 'cjk' } }
         # """)
-        # 创建 Entities 索引
+        # 创建 Entities 索引 (name + description + aliases)
         await connector.execute_query("""
-            CREATE FULLTEXT INDEX entitiesFulltext IF NOT EXISTS 
-            FOR (e:ExtractedEntity) ON EACH [e.name, e.description, e.aliases]
+            CREATE FULLTEXT INDEX entitiesFulltext IF NOT EXISTS FOR (e:ExtractedEntity) ON EACH [e.name, e.description, e.aliases]
             OPTIONS { indexConfig: { `fulltext.analyzer`: 'cjk' } }
         """)