fix(web): bring back the live shimmer on work log rows

[juliusmarminge]

#15033 removed the shimmer on active work log rows (live tool rows and the active work group header) as a perf fix. We've profiled that shimmer many times and it isn't a cost: it uses steps(30) rather than continuous repaints and pauses through --visible-animation-state while off-screen.

This reverses only the shimmer hunks from #15033: it restores the live-tool-shine utility and keyframes in index.css, the class on LiveActivityContent and WorkGroupHeader, and the visibility observer refs. The rest of #15033 is unchanged, including the scheduled-task status dot.

🤖 Generated with Claude Code

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[macroscopeapp]

Approvability

Verdict: Approved at 75adab8

Macroscope's review found this PR approvable — This is a narrowly scoped restoration of visual shimmer feedback for existing active work-log rows. The animation is limited to the relevant UI states and respects reduced-motion, forced-colors, document visibility, and viewport visibility safeguards, with no API, data, security, or deployment impact.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.9 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: 0ecb78e · PR result: 75adab8 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.