Add stable sort tiebreaker to prevent feed pagination duplicates

[mojoro]

Audit finding #54

When sorting by AI score during active analysis, cursor-based pagination can show duplicate jobs because scores change mid-scroll, shifting sort order.

Fix: Add a stable tiebreaker (e.g., createdAt or id) to the buildOrderBy function in src/lib/jobs.ts so the sort is deterministic even when scores update between page fetches.

Files: src/lib/jobs.ts, potentially src/app/(dashboard)/dashboard/actions.ts