Add operational health history for v0.44.0

[crypt0rr]

What changed

• Add persisted, bounded operational snapshots for queue age, provider failures, database size, backup age, restore status, and readiness degradation reasons.
• Surface the latest operational state and recent snapshots in the admin interface.
• Expose safe operational readiness headers without changing the existing healthy HTTP response contract.
• Add a non-destructive retention review threshold and documentation.
• Add release-documentation/version checks, CI wiring, and Renovate grouping for related Go tooling.

Why

This completes the v0.44 operational-visibility and recovery-governance work while keeping diagnostics household-scoped, redacted, and bounded. The readiness endpoint remains usable for orchestration, while headers and admin diagnostics distinguish database availability from operational degradation.

Validation

• gofmt and git diff check
• go test ./... -count=1
• go test -race ./... -count=1
• go vet ./...
• pinned lint and vulnerability checks
• make fmt-check tooling-check version-check VERSION=v0.44.0 coverage
• Docker test/runtime builds
• container startup, readiness, persistence, manual sync, and graceful-shutdown smoke test