* feat(backend): add stack update-preview endpoint for readiness board
Adds GET /api/stacks/:stackName/update-preview that returns per-image
semver diff, bump classification, and a stack-level summary powering
the Auto-Update readiness board.
- New UpdatePreviewService parses compose images, inspects local
digests, fetches remote digests and tag lists, and finds the
highest compatible semver tag.
- Major bumps are flagged blocked until human review; unknown bumps
rank below real semver so they cannot mask a major.
- Rollback target is reconstructed through parseImageRef to preserve
registry ports and drop the Docker Hub library/ prefix.
- Registry helpers (httpGet, auth token, digest, tag list, ref parse)
are extracted into registry-api.ts and shared with ImageUpdateService.
- 28 Vitest cases cover parse, selection, bump math, digest rebuilds,
blocked policy, and rollback target construction.
* feat(schedules): next-24h timeline, merge auto-update crud, add readiness board
Replace the flat task table with a Timeline view as the default, showing the
next 24 hours of scheduled work across four lanes (Restart, Update, Scan,
Prune) with a live now rail and per-firing pills. The All tasks tab preserves
the existing CRUD surface.
Merge Auto-update Stack into Schedules as a first-class action and replace the
standalone Auto-Update Policies view with a per-stack Readiness board that
surfaces version diffs, risk tags, changelog previews, and rollback targets
sourced from the stack update-preview endpoint.
Anso