Phase 3: Skills & Context — skill system, personal context, context layering

Backend:
- Skill model + migration (with FK on chats.skill_id)
- Personal + general skill CRUD services with access isolation
- Admin skill CRUD endpoints (POST/GET/PATCH/DELETE /admin/skills)
- User skill CRUD endpoints (POST/GET/PATCH/DELETE /skills/)
- Personal context GET/PUT at /users/me/context
- Extended context assembly: primary + personal context + skill prompt
- Chat creation/update now accepts skill_id with validation

Frontend:
- Skill selector dropdown in chat header (grouped: general + personal)
- Reusable skill editor form component
- Admin skills management page (/admin/skills)
- Personal skills page (/skills)
- Personal context editor page (/profile/context)
- Updated sidebar: Skills, My Context nav items + admin skills link
- English + Russian translations for all skill/context UI

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

GeneralPlan.md

@@ -214,8 +214,8 @@ Daily scheduled job (APScheduler, 8 AM) reviews each user's memory + recent docs
 - Summary: Chats + messages tables, chat CRUD, SSE streaming, Claude API integration, context assembly, frontend chat UI, admin context editor, chat limits
 
 ### Phase 3: Skills & Context
-- **Status**: NOT STARTED
-- [ ] Subplan created (`plans/phase-3-skills-context.md`)
+- **Status**: IN PROGRESS
+- [x] Subplan created (`plans/phase-3-skills-context.md`)
 - [ ] Phase completed
 - Summary: Skills + context_files tables, skills CRUD (general + personal), personal context CRUD, context layering, frontend skill selector + editors