refactor: migrate agent to Claude Agent SDK with MCP (#63)

Replace the custom 550-line Anthropic API implementation with the Claude Agent SDK (~260 lines). The agent now connects to the existing MCP server at /mcp instead of generating tools from OpenAPI spec.

Key changes:
- Use claude-agent-sdk query() with ClaudeAgentOptions for MCP server connection
- Remove openapi_to_claude_tools() and execute_api_tool() - MCP handles this
- Keep system prompt with country filtering guidance
- Simplify tests to match new implementation

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: nikhilwoodruff

pyproject.toml

@@ -24,6 +24,7 @@ dependencies = [
     "fastapi-mcp>=0.4.0",
     "modal>=0.68.0",
     "anthropic>=0.40.0",
+    "claude-agent-sdk>=0.1.0",
 ]
 
 [project.optional-dependencies]