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

deploy/k8s/prod/secrets/gateway-secrets.tpl.yaml

@@ -19,6 +19,7 @@ stringData:
     # LLM Provider API Keys
     llm_providers:
       deepinfra_api_key: "{{ op://AI Prod/Gateway/deepinfra_api_key }}"
+      anthropic_api_key: "{{ op://AI Prod/Gateway/anthropic_api_key }}"
 
     # Search API Keys
     search:
@@ -36,10 +37,6 @@ stringData:
     push:
       service_key: ""
 
-    # Qdrant API key (optional, for hosted Qdrant)
-    qdrant:
-      api_key: ""
-
     # Iceberg S3 credentials (must match minio-secret)
     iceberg:
       s3_access_key: "{{ op://AI Prod/MinIO/access_key }}"