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/src/harness/workflows/trading-request/config.yaml

@@ -14,6 +14,4 @@ approvalNodes:
 maxPositionPercent: 0.05  # 5% of portfolio max
 minRiskRewardRatio: 2.0   # Minimum 2:1 risk/reward
 
-# Model override (optional)
-model: claude-sonnet-4-6
 temperature: 0.2