feat(ms22-p2): add UserAgent CRUD endpoints

- UserAgentService with findAll, findOne, create, update, remove
- UserAgentController at /api/agents (authenticated, user-scoped)
- createFromTemplate endpoint to instantiate from AgentTemplate
- Update TASKS.md and MISSION-MANIFEST.md for P2-004

Task: MS22-P2-004

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/scratchpads/ms22-p2-named-agent-fleet-20260304.md

@@ -0,0 +1,23 @@
+# Mission Scratchpad — MS22-P2 Named Agent Fleet
+
+> Append-only log. NEVER delete entries. NEVER overwrite sections.
+> This is the orchestrator's working memory across sessions.
+
+## Original Mission Prompt
+
+```
+(Paste the mission prompt here on first session)
+```
+
+## Planning Decisions
+
+## Session Log
+
+| Session | Date       | Milestone   | Tasks Done             | Outcome                                                                                  |
+| ------- | ---------- | ----------- | ---------------------- | ---------------------------------------------------------------------------------------- |
+| 2       | 2026-03-04 | M3-UserCRUD | P2-004 in-progress     | Fixed CI security audit (multer>=2.1.1), merged PR #678 (Admin CRUD), starting User CRUD |
+| 1       | 2026-03-04 | M1+M2       | P2-001, P2-002, P2-003 | Schema, seed, and Admin CRUD complete                                                    |
+
+## Open Questions
+
+## Corrections