Iteration 2: add order tracking flow

[HimanM]

Summary

• add track_order support and normalize structured tracking payloads from MCP tool results
• render order tracking results in chat with a dedicated tracking card and add a tracking quick action
• add feature checklist markdowns for the remaining planned iterations and document iteration 2 verification

Verification

• python -m unittest tests.test_chat_route tests.test_tool_arg_sanitizer tests.test_provider_selection
• npm run lint
• npm run build
• Playwright fallback against http://localhost:3000 to verify missing-order-number flow and direct tracking request handling