TASK-001: Setup FastAPI project structure

- Fixed main.py to include all route routers (posts, users, comments, feed)
- Renamed app/models.py to app/schemas.py and split into proper schema modules
- Fixed schema imports in routes
- Updated app/models/__init__.py to properly export SQLAlchemy models
- Fixed database imports in route files
- App imports and runs correctly

app/schemas/feed.py

@@ -0,0 +1,14 @@
+"""Feed schemas for SocialPhoto API."""
+from typing import List
+
+from pydantic import BaseModel
+
+from app.schemas.post import PostResponse
+
+
+class FeedResponse(BaseModel):
+    """Response model for feed."""
+    posts: List[PostResponse]
+    total: int
+    limit: int
+    offset: int