fix(security): harden Trivy scan lifecycle, logging, and docs (#639)

* fix(security): harden Trivy scan lifecycle, logging, and docs

- Call TrivyService.initialize() at startup so capability state is
  accurate before first request; add periodic re-detect to the scheduler
  so newly installed Trivy binaries light up without a restart.
- Add markStaleScansAsFailed sweep (+ idx_vuln_scans_status index) to
  recover any scan row left in_progress after a crash or timeout; sweep
  runs before the paid-tier gate so every tier self-heals.
- Split scanImage persistence into beginScan/finishScan so the manual
  scan route owns a single code path and can return a scanId synchronously
  while work continues asynchronously.
- Validate image refs on /api/security/scan and /sbom via new utility;
  defense-in-depth against shell-metacharacter payloads.
- Dispatch a warning-level alert when a post-deploy scan fails so the
  operator has a user-visible path to the failure instead of a silent log.
- Share DIGEST_CACHE_TTL_MS and severity ordering across service and
  route layers; remove dead invalidateDetection().
- Add [Trivy:diag] logging gated behind developer_mode for support
  diagnostics; production logs unchanged.
- Frontend: defensive toast fallback chain, sr-only SheetDescription,
  and a truncation badge when the 500-item detail fetch is capped.
- Tests: extend trivy-service and vulnerability-db suites; add
  image-ref and severity unit tests.
- Docs: expand vulnerability-scanning troubleshooting with recovery,
  re-detect, and diagnostic-log guidance; link Dockerfile comment to
  trivy-setup.

* fix(security): drop unnecessary escape in image-ref forbidden-char regex

docs/operations/trivy-setup.mdx

@@ -150,6 +150,10 @@ After restarting Sencho with the mount in place:
 
 If the shield icon is missing, see the troubleshooting section below.
 
+### Runtime detection
+
+Sencho re-runs the `trivy --version` check every ten minutes from the background scheduler. You can install Trivy on a running host and scanning will light up on its own within that window. If the binary becomes unavailable at runtime, the UI hides itself in the same way.
+
 ## Troubleshooting
 
 ### Sencho does not detect Trivy