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/services/chat_service.py

@@ -9,7 +9,7 @@ from app.models.message import Message
 from app.models.user import User
 
 
-async def create_chat(db: AsyncSession, user: User, title: str | None = None) -> Chat:
+async def create_chat(db: AsyncSession, user: User, title: str | None = None, skill_id: uuid.UUID | None = None) -> Chat:
     count = await db.scalar(
         select(func.count()).select_from(Chat).where(
             Chat.user_id == user.id, Chat.is_archived == False  # noqa: E712
@@ -21,7 +21,7 @@ async def create_chat(db: AsyncSession, user: User, title: str | None = None) ->
             detail="Chat limit reached. Archive or delete existing chats.",
         )
 
-    chat = Chat(user_id=user.id, title=title or "New Chat")
+    chat = Chat(user_id=user.id, title=title or "New Chat", skill_id=skill_id)
     db.add(chat)
     await db.flush()
     return chat
@@ -51,12 +51,15 @@ async def get_chat(db: AsyncSession, chat_id: uuid.UUID, user_id: uuid.UUID) ->
 async def update_chat(
     db: AsyncSession, chat_id: uuid.UUID, user_id: uuid.UUID,
     title: str | None = None, is_archived: bool | None = None,
+    skill_id: uuid.UUID | None = None,
 ) -> Chat:
     chat = await get_chat(db, chat_id, user_id)
     if title is not None:
         chat.title = title
     if is_archived is not None:
         chat.is_archived = is_archived
+    if skill_id is not None:
+        chat.skill_id = skill_id
     await db.flush()
     return chat