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/schemas.py

@@ -0,0 +1,28 @@
+from pydantic import BaseModel, EmailStr
+
+
+class RegisterRequest(BaseModel):
+    email: EmailStr
+    password: str
+    tenant_name: str
+    telefon: str
+
+
+class LoginRequest(BaseModel):
+    email: EmailStr
+    password: str
+
+
+class TokenResponse(BaseModel):
+    access_token: str
+    token_type: str = "bearer"
+    tenant_id: str
+    plan: str
+
+
+class UserResponse(BaseModel):
+    id: str
+    email: str
+    tenant_id: str
+    plan: str
+    rol: str