feat: add volatile cache system for ephemeral data

Phase 2 of Memory Management System - volatile memory tier:

- VolatileCacheService: Redis-backed TTL storage
- Volatile router with full CRUD operations
- Predefined namespaces: weather, news, financial, transit, traffic,
  air_quality, sports, social, system, context, custom
- Each namespace has appropriate default TTL (1min to 1hr)
- Refresh schedule support via cron expressions
- Scheduler integration endpoint: GET /volatile/scheduled

Endpoints:
- GET/POST/DELETE /volatile/{namespace}/{key}
- GET/DELETE /volatile/{namespace}
- GET /volatile/stats
- GET /volatile/scheduled
- GET /volatile/namespaces

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/main.py

@@ -51,7 +51,7 @@ app.add_middleware(
 from src.routers import (
     wiki, tools, graph, vector, hybrid_rag, consolidation,
     ingestion, entity_linking, webhooks, rag_search, content,
-    maintenance
+    maintenance, volatile
 )
 
 app.include_router(wiki.router)
@@ -66,6 +66,7 @@ app.include_router(webhooks.router)
 app.include_router(rag_search.router)
 app.include_router(content.router)
 app.include_router(maintenance.router)
+app.include_router(volatile.router)
 
 # Mount static files directory for Wiki.js integration scripts
 static_dir = Path(__file__).parent.parent / "static"