ComfyUI: review follow-ups (I4 exc-leak, I5 image identity, minors)

[thinmintdev]

Final-review follow-ups on feat/comfyui-platform:

• I4: /workflows/{name}/launch 500 path echoes str(exc); _find_workflow unguarded — add name validation, don't leak exceptions.
• I5: Phase 6.1 not done — manifest/SEED_PROFILES/profiles.toml/img.toml not repointed (image build deferred); image identity diverges (slot vs comfy-up.sh vs manifest) — reconcile/document.
• Selections.comfyui_defaults sidecar: future ComfyUISelection refactor; hoist local import.
• installer repair if-unit==comfyui → _REPAIR_HANDLERS dispatch table when 2nd container-service added.
• UI: logs via alert() → log drawer; preview stale mid-render.
  Full review: /tmp/comfyui-sdd/final-review.md (local).