Page Code Animation history and refresh from job events

[atomantic]

What changed

Code Animation now opens with a compact, deterministic 50-job page and loads older jobs on demand. The paged route caps reads at 100, returns collection-wide counts, and omits full concepts; bookmarked job details still load through the existing detail route. Query-less callers retain their array response.

The gallery no longer polls every ten seconds. Durable job start, completion, failure, and restart reconciliation emit a scoped invalidation; the page refreshes its first page on changes and socket reconnect while keeping loaded history. The selected running job keeps its existing detail poll.

Validation

• Focused server and client tests pass, covering 1,000 synthetic jobs, equal-timestamp cursor continuation, cap and invalid cursor, legacy response, interrupted-job recovery, first-page rendering, a simulated 60-second visible idle period, socket change, and reconnect.
• npm run pregate passed. The configured tool-free Codex TUI review returned no findings.
• Synthetic 1,000-job JSON sizes: legacy full list 2,142,891 bytes; first compact 50-row page 6,596 bytes. The simulated idle minute made zero further archive requests and received zero socket frames. These are fixture payload bytes, not measured live HTTP wire bytes or browser network capture; CI will validate the integration.

Closes #8517