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>

backend/app/api/v1/users.py

@@ -0,0 +1,33 @@
+from typing import Annotated
+
+from fastapi import APIRouter, Depends
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.api.deps import get_current_user
+from app.database import get_db
+from app.models.user import User
+from app.schemas.chat import ContextFileResponse, UpdateContextRequest
+from app.services import context_service
+
+router = APIRouter(prefix="/users", tags=["users"])
+
+
+@router.get("/me/context", response_model=ContextFileResponse | None)
+async def get_personal_context(
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    ctx = await context_service.get_personal_context(db, user.id)
+    if not ctx:
+        return None
+    return ContextFileResponse.model_validate(ctx)
+
+
+@router.put("/me/context", response_model=ContextFileResponse)
+async def update_personal_context(
+    data: UpdateContextRequest,
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    ctx = await context_service.upsert_personal_context(db, user.id, data.content)
+    return ContextFileResponse.model_validate(ctx)