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/context_service.py

@@ -23,6 +23,34 @@ async def get_primary_context(db: AsyncSession) -> ContextFile | None:
     return result.scalar_one_or_none()
 
 
+async def get_personal_context(db: AsyncSession, user_id: uuid.UUID) -> ContextFile | None:
+    result = await db.execute(
+        select(ContextFile).where(ContextFile.type == "personal", ContextFile.user_id == user_id)
+    )
+    return result.scalar_one_or_none()
+
+
+async def upsert_personal_context(
+    db: AsyncSession, user_id: uuid.UUID, content: str
+) -> ContextFile:
+    ctx = await get_personal_context(db, user_id)
+    if ctx:
+        ctx.content = content
+        ctx.version = ctx.version + 1
+        ctx.updated_by = user_id
+    else:
+        ctx = ContextFile(
+            type="personal",
+            user_id=user_id,
+            content=content,
+            version=1,
+            updated_by=user_id,
+        )
+        db.add(ctx)
+    await db.flush()
+    return ctx
+
+
 async def upsert_primary_context(
     db: AsyncSession, content: str, admin_user_id: uuid.UUID
 ) -> ContextFile: