Redesign repo list rows with activity sparklines

[kevincodex1]

Description

Redesigns the repository list rows and adds a GitHub-style commit-activity graph.

Rows go from a dense single line (~44px) to a taller two-line layout (~95px):
repo name + pills on line one, full-width description on line two, updated time
and stars stacked in a right-aligned meta column. The squeezed description/branch
grid columns are removed (branch was already shown as a pill).

Each row gains an activity sparkline (md+ viewports): a dependency-free
110×28 SVG bar chart of weekly commit counts over the last 12 weeks — past weeks
in a de-emphasis tone, the current week in the warm accent. The value is exposed
via aria-label; sums at the node's 30-commit API cap read as a floor ("30+ commits").

Loading is node-friendly: useRepoActivity fetches /commits only once a row
scrolls near the viewport (IntersectionObserver, 200px margin), through a 2-slot
concurrency pool (the node limits concurrent connections), with a session cache.
Hover-prefetched repos (repoCache) resolve without any fetch via the new
RepoCommit.dateRaw field.

Known limitation: the node returns at most 30 commits, so hyperactive repos
collapse into a single current-week bar. The real fix is server-side weekly
buckets on the list endpoint — a good candidate to bundle with the pending
q=/sort= node deploy.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that changes existing behavior)
• Refactor / code quality (no behavior change)
• Documentation
• Tests / CI

How was this tested?

• 8 new unit tests for the week-bucketing logic (src/lib/activity.test.ts);
  full suite: 68 tests passing.
• Driven end-to-end with Playwright against the live node (dev proxy):
  • Max in-flight /commits requests observed: 2 (concurrency cap holds).
  • Only near-viewport rows fetch: 6 requests on load, 12 more after paging to
    page 2 — not one per row.
  • Sparklines hidden below md (0 visible at 390px); rows stack cleanly on mobile.
  • Verified light and dark themes via the app's own theme persistence.
  • Zero console errors.

Screenshots

Checklist

• npm run lint passes
• npm test passes
• npm run build passes (includes typecheck)
• New logic in src/lib/ has colocated unit tests
• I kept the change focused on a single concern