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/alembic/versions/88221cd8e1c3_initial_tenants_users.py

@@ -0,0 +1,62 @@
+"""initial_tenants_users
+
+Revision ID: 88221cd8e1c3
+Revises: 
+Create Date: 2026-03-13 17:25:56.158996
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '88221cd8e1c3'
+down_revision: Union[str, None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('tenants',
+    sa.Column('nume', sa.String(length=200), nullable=False),
+    sa.Column('cui', sa.String(length=20), nullable=True),
+    sa.Column('reg_com', sa.String(length=30), nullable=True),
+    sa.Column('adresa', sa.Text(), nullable=True),
+    sa.Column('telefon', sa.String(length=20), nullable=True),
+    sa.Column('email', sa.String(length=200), nullable=True),
+    sa.Column('iban', sa.String(length=34), nullable=True),
+    sa.Column('banca', sa.String(length=100), nullable=True),
+    sa.Column('plan', sa.String(length=20), nullable=False),
+    sa.Column('trial_expires_at', sa.Text(), nullable=True),
+    sa.Column('id', sa.String(length=36), nullable=False),
+    sa.Column('created_at', sa.Text(), nullable=False),
+    sa.Column('updated_at', sa.Text(), nullable=False),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_table('users',
+    sa.Column('email', sa.String(length=200), nullable=False),
+    sa.Column('password_hash', sa.String(length=200), nullable=False),
+    sa.Column('nume', sa.String(length=200), nullable=False),
+    sa.Column('rol', sa.String(length=20), nullable=False),
+    sa.Column('activ', sa.Boolean(), nullable=False),
+    sa.Column('id', sa.String(length=36), nullable=False),
+    sa.Column('tenant_id', sa.String(length=36), nullable=False),
+    sa.Column('created_at', sa.Text(), nullable=False),
+    sa.Column('updated_at', sa.Text(), nullable=False),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_users_email'), 'users', ['email'], unique=True)
+    op.create_index(op.f('ix_users_tenant_id'), 'users', ['tenant_id'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f('ix_users_tenant_id'), table_name='users')
+    op.drop_index(op.f('ix_users_email'), table_name='users')
+    op.drop_table('users')
+    op.drop_table('tenants')
+    # ### end Alembic commands ###