feat(watchlist): add source filter chips to Issues tab

[Khaostica]

Summary

Adds three multi-select chips (Starred/Miner/Repo) to the Watchlist → Issues tab toolbar, closing the parity gap with the Pull Requests tab where these chips shipped in #1072. Colors and labels mirror the existing source badges (#789, #799). All three are selected by default, preserving the auto-show behavior — toggling chips off hides Issues whose only remaining sources are deselected (union-based, same semantics as the PRs tab).

Reuses usePrSourceFilter (persistence under gittensor.watchlist.prs-source-filter.v1, cross-tab storage-event sync — same key as the PRs tab, so source-filter selection is shared across both tabs and reloads) and the sourcesByKey map already computed inside IssuesList. No new hooks, no new components. One file touched: src/pages/WatchlistPage.tsx (+64/-5).

Related Issues

None

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Screenshots

Before:

After:

Additional Video:

Issues.Filter.Chips.-.After.mp4

Checklist

• New components are modularized/separated where sensible
• Uses predefined theme (e.g. no hardcoded colors)
• Responsive/mobile checked
• Tested against the test API
• npm run format and npm run lint:fix have been run
• npm run build passes
• Screenshots included for any UI/visual changes