feat(backend): FastAPI + libSQL + auth register/login/me + tests (TDD)

- FastAPI app with lifespan, CORS, health endpoint
- SQLAlchemy 2.0 async with aiosqlite, Base/UUIDMixin/TenantMixin/TimestampMixin
- Tenant and User models with multi-tenant isolation
- Auth: register (creates tenant+user), login, /me endpoint
- JWT HS256 tokens, bcrypt password hashing
- Alembic async setup with initial migration
- 6 passing tests (register, login, wrong password, me, no token, health)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/auth/service.py

@@ -0,0 +1,62 @@
+from datetime import UTC, datetime, timedelta
+
+from jose import jwt
+import bcrypt
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.config import settings
+from app.db.base import uuid7
+from app.db.models.tenant import Tenant
+from app.db.models.user import User
+
+
+def hash_password(p: str) -> str:
+    return bcrypt.hashpw(p.encode(), bcrypt.gensalt()).decode()
+
+
+def verify_password(plain: str, hashed: str) -> bool:
+    return bcrypt.checkpw(plain.encode(), hashed.encode())
+
+
+def create_token(user_id: str, tenant_id: str, plan: str) -> str:
+    exp = datetime.now(UTC) + timedelta(days=settings.ACCESS_TOKEN_EXPIRE_DAYS)
+    return jwt.encode(
+        {"sub": user_id, "tenant_id": tenant_id, "plan": plan, "exp": exp},
+        settings.SECRET_KEY,
+        algorithm="HS256",
+    )
+
+
+async def register(
+    db: AsyncSession, email: str, password: str, tenant_name: str, telefon: str
+):
+    trial_exp = (datetime.now(UTC) + timedelta(days=settings.TRIAL_DAYS)).isoformat()
+    tenant = Tenant(
+        id=uuid7(),
+        nume=tenant_name,
+        telefon=telefon,
+        plan="trial",
+        trial_expires_at=trial_exp,
+    )
+    db.add(tenant)
+    user = User(
+        id=uuid7(),
+        tenant_id=tenant.id,
+        email=email,
+        password_hash=hash_password(password),
+        nume=email.split("@")[0],
+        rol="owner",
+    )
+    db.add(user)
+    await db.commit()
+    return user, tenant
+
+
+async def authenticate(db: AsyncSession, email: str, password: str):
+    r = await db.execute(select(User).where(User.email == email))
+    user = r.scalar_one_or_none()
+    if not user or not verify_password(password, user.password_hash):
+        return None, None
+    r = await db.execute(select(Tenant).where(Tenant.id == user.tenant_id))
+    return user, r.scalar_one_or_none()