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/post.py

@@ -0,0 +1,48 @@
+"""Post schemas for SocialPhoto API."""
+from datetime import datetime
+from typing import Optional
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class PostCreate(BaseModel):
+    """Request model for creating a post."""
+    caption: Optional[str] = ""
+
+
+class PostResponse(BaseModel):
+    """Response model for post data."""
+    id: int
+    user_id: int
+    username: str
+    image_url: str
+    caption: str
+    likes_count: int
+    dislikes_count: int
+    comments_count: int
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class PostDetail(PostResponse):
+    """Detailed post response with user info."""
+    user: "UserResponse"  # noqa: F821
+
+
+class CommentCreate(BaseModel):
+    """Request model for creating a comment."""
+    content: str = Field(..., min_length=1, max_length=500)
+
+
+class CommentResponse(BaseModel):
+    """Response model for comment data."""
+    id: int
+    post_id: int
+    user_id: int
+    username: str
+    content: str
+    likes_count: int
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)