[dgsienko]

Fixes from a full-repo slop audit, web half.

• Dead code: the never-set showIgnored state, the Diff Stats Bar CSS block, settings close transitions, the unused warn colors, and guards for states callers never produce
• Keybinding defaults are defined once in lib/keys.js (they were in four places)
• sendJson and commentUrl helpers replace seven hand-built JSON fetches
• DiffViewer and SplitDiffViewer share the comment thread, comment box and selection button through components/CommentThread.js
• One latest-value mechanism (mirror refs), not two
• app.js goes from 1188 to 637 lines. The split moves its hooks into lib/ (live events, comments, keyboard, agent, scroll, copy, search, appearance, session save) and the empty and loading states into a component.

Two behavior changes, both intended. The r key could refetch the file list for a stale view, and now uses the current one. Settings changes apply right away, before the save returns.

Checked in a browser against a scratch repo: file switching, all three diff views, comments, search, the palette, the shortcut overlay, rebinding a key, and mark reviewed. There were no console errors.