TML-563: remediate UI/UX review findings

[SeasonsChange422]

Summary

• Reworks the Studio shell around container-responsive editor tabs, a compact mobile toolbar, a larger scene workspace, and a collapsed mobile host log.
• Adds a shared accessible modal boundary with focus containment/restoration and host-shortcut isolation.
• Replaces single-character controls with Lucide icons, increases interaction targets, and aligns disabled/focus styling with Studio tokens.

Review Findings

1. Modal focus trap, Escape handling, shortcut isolation, inert background, and visible focus restoration are implemented.
2. Editor layout now responds to its embed container with Scene, Objects, and Properties tabs.
3. Narrow/mobile toolbar and host layout preserve a usable scene viewport.
4. Scene, view, property, and naming controls expose accessible names.
5. Timeline ruler, tracks, shots, and keyframes are keyboard operable with conventional slider keys.
6. Desktop/touch targets are enlarged and tree actions remain discoverable.
7. Disabled timeline/tree contrast is corrected.
8. Unicode/single-character controls are replaced by Lucide icons.
9. Mock plugin controls inherit Studio surface, border, text, focus, and disabled tokens.

Verification

• npm test: 98 test files passed, 1 skipped; 1,634 tests passed.
• Focused Studio unit regressions: 32/32 passed.
• Final Chromium Studio/UI regression group: 16/16 passed, including axe, focus restoration, menu/tab keys, token styling, and desktop/mobile canvas-pixel checks.
• Existing relevant Chromium cases: 104 green across split runs; the final all-spec aggregate attempt hit the local five-minute command limit and is not claimed as a separate pass.
• Screenshot generator: 1/1 passed and refreshed all 12 before/after pairs.
• npm run typecheck: all six workspaces passed.
• npm run lint: 0 errors; 3 pre-existing Fast Refresh warnings.
• npm run build: all packages passed (existing Lucide directive and large host chunk warnings remain).
• npm run licenses:generate: deterministic second run; lucide-react is present in docs/THIRD_PARTY_NOTICES.md.
• git diff --check: passed.

Evidence

See the exact state/viewport matrix in docs/evidence/tml-563/README.md.

Merge Gate

Do not merge until the original reviewer re-reviews this PR and returns PASS.

[SeasonsChange422]

TML-563 review follow-up

Updated this PR with commit f0ae573 to close the eight findings from the latest HOLD review:

• document-scoped modal isolation and top-modal routing across host siblings, open ShadowRoots, and two Studio instances;
• stable focus across plugin enable, disable, and failure transitions;
• container behavior at the 900/901 and 1100/1101 boundaries;
• 375px shot controls, valid 0.1s fit geometry, keyframe lanes, and storyboard targets;
• 667x375 expanded host-log layout while preserving Scene and Timeline.

Verification:

• npm run typecheck: passed
• npm run lint: passed (0 errors; 3 existing Fast Refresh warnings)
• focused Vitest: 32/32 passed
• Chromium UI/UX regression: 17/17 passed
• screenshot generation: 1/1 passed (24 isolated states)
• npm run build: passed
• completion code review: PASS, no Critical or Important findings

Before/after evidence and the exact state/viewport matrix are in docs/evidence/tml-563/README.md. State 15 now explicitly exercises the valid minimum 0.1s shot.

This PR has not been merged and is ready for the original reviewer to re-run the recorded failure states.