[codex] Add watchlist research notes

[judefluen-coder]

Summary

• Add local watchlist research fields: priority, tags, thesis, and next review date.
• Show editable watchlist notes in both company detail and the watchlist panel.
• Include research-note fields in watchlist JSON/CSV exports and migrate existing local records safely.

Why

The watchlist becomes more useful as a stock research workspace when users can record why a company is being tracked and when to revisit the evidence.

Validation

• npm run smoke
• npm run validate:tabular
• npm run validate:example
• npm run build
• git diff --check
• Playwright desktop flow: add 星阵芯科 to watchlist, edit priority/tags/thesis/next review date, verify localStorage
• Playwright mobile 390x844 check: watch memo is single-column with no horizontal overflow