feat(web): show running indicator for active sessions in sidebar

[cal-gooo]

Summary

Adds a subtle "alive" marker to each running session in the sidebar so users can tell at a glance which sessions are busy without opening them.

• SessionRunningIndicator component rendered next to the title for running sessions in both list and grouped views
• A session is considered running when its session.status.state is busy or restarting
• Three-layer composition, all CSS-only (no Framer Motion — many rows may animate at once): solid emerald core with drop-shadow, soft breathing halo, and a rotating orbital arc (conic-gradient + radial mask). Durations are intentionally offset (1.4s / 1.9s / 2.4s) so the layers never re-sync — gives it an organic "alive" feel rather than a mechanical spinner
• Uses new --session-running* CSS tokens with light/dark variants so it matches the existing shadcn-style theme
• Respects prefers-reduced-motion
• Accessible: <output role="status" aria-label="Session is running">

Preview

Left half is the light theme, right half is dark. Top: a sample sidebar with running and non-running rows interleaved. Bottom: the indicator enlarged so you can see the three animation layers.

Testing

Adds vitest + @testing-library/react to web/ (no prior JS test runner existed) and a SessionRunningIndicator test suite covering default label, semantic element, base class + core layer, custom label, and className merging.

web$ npm test
 Test Files  1 passed (1)
      Tests  5 passed (5)

Test plan

• cd web && npm test — vitest suite passes
• cd web && npm run typecheck — clean
• cd web && npm run lint — clean (two pre-existing useSimplifiedLogicExpression errors in approval-dialog.tsx and session-files-panel.tsx were auto-fixed; behavior unchanged)
• cd web && npm run build — clean
• Manual: start a chat in a session and confirm the indicator appears on that row in the sidebar, then disappears after the turn completes

🤖 Generated with Claude Code

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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