Separate skills state completely per user

- All skill toggles are now per-user (except multi-agent-orchestrator
  which remains global). Admin toggle without a target username defaults
  to their own per-user state instead of the global file.
- GET /api/skills defaults to the requesting user's own state (previously
  returned global state when no ?username= param was given).
- Add SkillsManager.initUserSkillsState(): creates per-user
  skills_state.json from global defaults if missing — called on user
  creation and on every login as a safety net for existing accounts.
- Create initial per-user skills_state.json for cherry and jasmine.

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

.smallclaw/users/cherry/skills_state.json

@@ -0,0 +1,10 @@
+{
+  "lawyer": false,
+  "psychiatrist": false,
+  "musician": false,
+  "accountant": false,
+  "investor": false,
+  "counselor": false,
+  "meteorologist": true,
+  "presenter": true
+}

.smallclaw/users/jasmine/skills_state.json

@@ -0,0 +1,10 @@
+{
+  "lawyer": false,
+  "psychiatrist": false,
+  "musician": false,
+  "accountant": false,
+  "investor": true,
+  "counselor": false,
+  "meteorologist": true,
+  "presenter": false
+}