feat: add @tag model override support and remove Qdrant dependencies

- Add model-tags parser for @Tag syntax in chat messages
- Support Anthropic models (Sonnet, Haiku, Opus) via @tag
- Remove Qdrant vector database from infrastructure and configs
- Simplify license model config to use null fallbacks
- Add greeting stream after model switch via @tag
- Fix protobuf field names to camelCase for v7 compatibility
- Add 429 rate limit retry logic with exponential backoff
- Remove RAG references from agent harness documentation

gateway/package.json

@@ -19,6 +19,7 @@
     "@langchain/community": "^1.1.27",
     "@langchain/core": "latest",
     "@langchain/langgraph": "latest",
+    "@langchain/anthropic": "latest",
     "@langchain/openai": "^1.4.2",
     "@modelcontextprotocol/sdk": "^1.0.4",
     "@types/pdf-parse": "^1.1.5",