v0.3.0: finish Async Embedding Gateway — mark-vector-stale, cron, defskill, ROADMAP updates

- Add mark-vector-stale(id, content): sets :vector to :pending, queues for re-embed
- Register cron job (embed-all-pending every 10m on :reflex tier via orchestrator)
- Add defskill :passepartout-system-model-embedding (priority 70)
- Remove embedding from topological-sort exclusion list in core-skills
- Export mark-vector-stale in core-defpackage
- Contract: items 4 (mark-vector-stale) and 5 (cron registration)
- Test: test-mark-vector-stale (5 checks)
- ROADMAP: mark Context Manager, Async Embedding Gateway, TUI Experience as DONE
- All v0.3.0 items now complete. Total: 5 suites, 85 checks, 0 failures

org/core-defpackage.org

@@ -117,6 +117,7 @@ The package definition. All public symbols are exported here.
        #:embed-all-pending
        #:embedding-backend-hashing
        #:embeddings-compute
+       #:mark-vector-stale
      #:skill
    #:skill-name
    #:skill-priority