feat: implement Instagram clone SocialPhoto API

- FastAPI backend with SQLite database
- JWT authentication (register, login)
- User profiles with follow/unfollow
- Posts with image upload and likes/dislikes
- Comments with likes
- Global and personalized feed
- Comprehensive pytest test suite (37 tests)

TASK-ID: 758f4029-702

app/auth.py

@@ -0,0 +1,66 @@
+"""Authentication utilities for SocialPhoto."""
+from datetime import datetime, timedelta, timezone
+from typing import Optional
+
+from fastapi import Depends, HTTPException, status
+from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
+from jose import JWTError, jwt
+from passlib.context import CryptContext
+
+# Configuration
+SECRET_KEY = "your-secret-key-change-in-production"  # TODO: Move to env
+ALGORITHM = "HS256"
+ACCESS_TOKEN_EXPIRE_HOURS = 24
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+security = HTTPBearer()
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    """Verify a password against its hash."""
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def hash_password(password: str) -> str:
+    """Hash a password using bcrypt."""
+    return pwd_context.hash(password)
+
+
+def create_access_token(data: dict, expires_delta: Optional[timedelta] = None) -> str:
+    """Create a JWT access token."""
+    to_encode = data.copy()
+    if expires_delta:
+        expire = datetime.now(timezone.utc) + expires_delta
+    else:
+        expire = datetime.now(timezone.utc) + timedelta(hours=ACCESS_TOKEN_EXPIRE_HOURS)
+    to_encode.update({"exp": expire})
+    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
+    return encoded_jwt
+
+
+def decode_token(token: str) -> dict:
+    """Decode and verify a JWT token."""
+    try:
+        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+        return payload
+    except JWTError:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid authentication credentials",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+
+
+async def get_current_user_id(
+    credentials: HTTPAuthorizationCredentials = Depends(security),
+) -> int:
+    """Extract user ID from JWT token."""
+    token = credentials.credentials
+    payload = decode_token(token)
+    user_id: int = payload.get("sub")
+    if user_id is None:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid token payload",
+        )
+    return int(user_id)