polish(renderer): captionStyle variants, wired track colors, token cleanup, dead CSS, a11y

[thisiscsim]

Summary

Audit roadmap Phase 6 (final polish).

• captionStyle variants — the theme's caption style was decorative: karaoke/block/word all rendered the single active word. Now word keeps the single-word look, block shows the current phrase, and karaoke shows the phrase with the active word highlighted in the accent color. Phrase grouping breaks on a speech pause (>0.6s) or a length cap. captionLineAt/activeWordIndexAt are pure and unit-tested (6 cases).
• Wired timeline track colors — the markup emitted tl-chip-video/-text/-audio but no CSS consumed the --action-* design tokens (chips all rendered generic gray). Now tinted per type from the tokens.
• Raw hex → token — the recording button's inline #c0392b → --foreground-danger.
• Dead CSS removed (~120 lines from styles.css: .kv, .prompt, .dropzone*, .audio-actions, .swatch*, .style-row*, .critique*, .field(s)/.field-row, .mt) — each verified to have zero JSX references (.input.compact, .field-label, .section-h are still used and kept).
• Accessibility — ui/Modal gains aria-modal, initial focus into the dialog, a Tab focus trap, and focus restore to the opener on close; Home project/album tiles and timeline clips are keyboard-operable (Enter/Space activate; clips expose role/aria-label/aria-pressed).

Renderer-only — no dev-server restart needed.

Deferred (noted, not blocking): full arrow-key clip nudging on the timeline, and merging ExportModal/SettingsModal's bespoke overlays onto ui/Modal (both are larger and carry more visual-regression risk than the rest of this PR).

Test plan

• 6 caption-grouping tests (word index binary search + phrase grouping/pause-break); 126 total
• typecheck / lint / format / build green
• Removed CSS selectors confirmed unreferenced across components/ + App.tsx
• Manual (post-merge): switch captionStyle in the Inspector and scrub — word vs phrase vs karaoke differ; video/text/audio chips are tinted; Tab is trapped in dialogs and returns to the opener on close

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