[perf] Replace StatusBadge inline styles with CSS module

[github-actions]

Tier 2 — Render Performance: Eliminate per-render style object allocation

Baseline

StatusBadge spread two plain objects on every render:

// Before: creates a new object on every render call
<span className="f6" style=\{\{ ...baseStyles, ...variantStyles[variant] }}>

Two module-level React.CSSProperties objects (baseStyles, variantStyles) were defined as constants but then spread into a new object on every render, which:

• Allocates heap memory every render cycle
• Prevents the React reconciler from short-circuiting style diffing (new object reference each time)
• Keeps inline JS-side style computation when CSS handles it better

StatusBadge is used widely — every AI activity event, TTFT badge, conversation badge, model badge, and MCP tools badge renders it. In the AIActivityPanel (which shows streaming data), this component can re-render many times per second.

Fix

Moved all styles to a CSS module (StatusBadge.module.css) with one base class (.badge) and four variant classes (.success, .warning, .info, .neutral), then replaced the inline style with static class name lookup:

// After: zero object allocation — className string is a static reference
<span className={`\$\{styles.badge} \$\{styles[variant]}`}>
```

**Changes:**
- `src/components/StatusBadge/StatusBadge.module.css` — new CSS module with base + variant styles using Primer CSS custom properties
- `src/components/StatusBadge/index.tsx` — removed `baseStyles`/`variantStyles` constants and the `style` prop; added `styles` import; 30 lines deleted

### Result

- Zero heap object allocation per render in `StatusBadge`
- CSS styles cached by the browser and applied via class lookup (O(1))
- Smaller JS bundle: moved ~20 lines of style data from JS to CSS
- TypeScript clean (`npx tsc --noEmit` — no new errors)
- ESLint clean (`npm run lint` — passes)

### Verification

```
npx tsc --noEmit  ✅ no new errors
npm run lint      ✅ passes

Note: npm test and npm run build fail in this CI environment due to pre-existing issues: missing GITHUB_TOKEN auth for some test cases, and a native module resolution error in @github/copilot-sdk. Neither is related to this change.

Generated by Daily Performance Improver

[github-actions]

Pull request created: #118