[perf] perf: replace static inline styles in Dashboard loading states with CSS classes

[github-actions]

Summary

Replaces 2 static inline style=\{\{}} objects in Dashboard components with reusable CSS module classes. This is a Tier 2 render performance fix.

---

Tier: 2 — Render & API Performance

Baseline: Both components had static inline style objects evaluated on every render:

File	Location	Properties
profile-activity-section.tsx	line 50–55	display, alignItems, justifyContent, padding (4 props)
welcome-section.tsx	line 21	display, verticalAlign (2 props)

Fix:

Added two new utility classes to Dashboard.module.css:

/* Loading spinner centered in a section */
.sectionLoadingCenter {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 3rem 0;
}

/* Inline skeleton placeholder (e.g. username in welcome heading) */
.skeletonInline {
  display: inline-block;
  vertical-align: middle;
}
```

- `profile-activity-section.tsx`: loading spinner `(div)` uses `.sectionLoadingCenter`
- `welcome-section.tsx`: `(SkeletonBox)` uses `.skeletonInline`

**Why this improves performance:**

Static inline `style=\{\{ }}` object literals create a **new JavaScript object on every render**. React must shallow-compare the old and new style objects, then apply individual style property updates. CSS module classes are parsed once by the browser at stylesheet load time and referenced by class name — no object allocation, no per-property comparison.

**Result:** Eliminated 6 inline style properties across 2 Dashboard components (both on the hot `/` dashboard route) with zero allocation cost at render time.

**Verification:**

```
npx tsc --noEmit  ✅ clean
npm run lint      ✅ clean
npm test          ✅ 60 test files pass (3 pre-existing failures in github/client.test.ts require GITHUB_TOKEN env var, unrelated to this change)

Files changed:

• src/components/Dashboard/Dashboard.module.css — added .sectionLoadingCenter and .skeletonInline
• src/components/Dashboard/profile-activity-section.tsx — removed 4-property inline style
• src/components/Dashboard/welcome-section.tsx — removed 2-property inline style

Generated by Daily Performance Improver