[codex] Add A-share watchlist decision dashboard

[3105138391-sketch]

Summary

• Add deterministic A-share decision rules for watchlist and portfolio monitoring.
• Add a protected watchlist signal API and a React Today Watchlist page.
• Wire the new page into navigation and API exports.

Validation

• python -m pytest tests/test_a_share_decision.py -q
• pnpm build
• Browser QA on http://127.0.0.1:5183/watchlist, including refresh interaction and mobile viewport DOM check.

Notes

• The feature is advisory only. It outputs decision labels, reasons, risks, confirmation conditions, and invalidation conditions. It does not perform automatic trading.