feat: implementare JWT Bearer authentication pe toți routers [C-01]

Implementare completă a autentificării Bearer token:
- Creiez backend/auth.py: funcții JWT (create_access_token, get_current_user, get_current_admin)
- Modific /users/login: returnează TokenResponse cu JWT token și expirare 8h
- Adaug Depends(get_current_user) pe toate endpoint-urile API
- [M-02] user_id extras din JWT token, nu din request body
- [L-01] Token cu exp claim pentru sesiuni frontend

Acces endpoints-uri:
- GET/POST /users/: authenticated users
- POST /users/: admin only
- PUT /users/{id}, DELETE /users/{id}, /ldap-config, /test-ldap: admin only
- Toți routers (items, operations, categories): authenticated users minimum

Modificări dependențe:
- Adaug: python-jose[cryptography]>=3.3.0, slowapi>=0.1.9 (pentru H-02 rate limiting)

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

backend/auth.py

@@ -0,0 +1,100 @@
+"""
+[C-01] JWT Authentication Module
+Implementare Bearer token authentication pentru API endpoints.
+"""
+import os
+from datetime import datetime, timedelta, timezone
+from typing import Optional
+from fastapi import Depends, HTTPException, status
+from fastapi.security import HTTPBearer, HTTPAuthCredentials
+from jose import JWTError, jwt
+from pydantic import BaseModel
+
+# Configuration
+SECRET_KEY = os.environ.get("JWT_SECRET_KEY")
+if not SECRET_KEY:
+    # Genereaza o cheie de fallback pentru dev (NU PENTRU PRODUCȚIE)
+    import secrets
+    SECRET_KEY = secrets.token_urlsafe(32)
+    import sys
+    print(f"[WARNING] JWT_SECRET_KEY not set. Generated ephemeral key: {SECRET_KEY[:20]}...", file=sys.stderr)
+
+ALGORITHM = "HS256"
+ACCESS_TOKEN_EXPIRE_MINUTES = 480  # 8 hours
+
+security = HTTPBearer()
+
+
+class TokenData(BaseModel):
+    sub: int  # user_id
+    username: str
+    role: str
+    exp: datetime
+
+
+class TokenResponse(BaseModel):
+    access_token: str
+    token_type: str
+    user_id: int
+    username: str
+    role: str
+
+
+def create_access_token(user_id: int, username: str, role: str, expires_delta: Optional[timedelta] = None):
+    """Create JWT token with expiration."""
+    if expires_delta:
+        expire = datetime.now(timezone.utc) + expires_delta
+    else:
+        expire = datetime.now(timezone.utc) + timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
+
+    to_encode = {
+        "sub": user_id,
+        "username": username,
+        "role": role,
+        "exp": expire,
+        "iat": datetime.now(timezone.utc)
+    }
+    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
+    return encoded_jwt
+
+
+async def get_current_user(credentials: HTTPAuthCredentials = Depends(security)):
+    """
+    Dependency que valideaza JWT token din Authorization header.
+    Returneaza TokenData cu user_id, username, role.
+    """
+    token = credentials.credentials
+    try:
+        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+        user_id: int = payload.get("sub")
+        username: str = payload.get("username")
+        role: str = payload.get("role")
+
+        if user_id is None or username is None:
+            raise HTTPException(
+                status_code=status.HTTP_401_UNAUTHORIZED,
+                detail="Invalid token claims"
+            )
+        token_data = TokenData(
+            sub=user_id,
+            username=username,
+            role=role,
+            exp=datetime.fromtimestamp(payload.get("exp"), tz=timezone.utc)
+        )
+    except JWTError:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid authentication credentials",
+            headers={"WWW-Authenticate": "Bearer"},
+        )
+    return token_data
+
+
+async def get_current_admin(current_user: TokenData = Depends(get_current_user)):
+    """Dependency que verifica daca user-ul are rol 'admin'."""
+    if current_user.role != "admin":
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Admin role required"
+        )
+    return current_user