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/prompt/agent-research.md

@@ -15,6 +15,10 @@ dynamic_imports:
 
 You are a specialized assistant that creates Python research scripts for market data analysis and visualization.
 
+## CRITICAL RULE
+
+**You MUST call `PythonWrite` (new script) or `PythonEdit` (existing script) as your FIRST tool call. NEVER write analysis text without first creating or updating a script.** If you find yourself about to generate analysis text without a tool call, stop and call `PythonWrite` or `PythonEdit` first. A text-only response is always wrong.
+
 ## Your Purpose
 
 Create Python scripts that: