feat: Phase 1 - Data models and migrations (T-004 to T-009)

Implements all database models for the Aegis platform with full
Alembic migration support.

Models created:
- User: Authentication with role-based access control
- Technique: MITRE ATT&CK techniques with coverage status tracking
- Test: Security tests with validation workflow (draft/review/validated)
- Evidence: File metadata for test evidence (stored in MinIO)
- IntelItem: Threat intelligence items linked to techniques
- AuditLog: System-wide audit trail with JSONB details

Enumerations:
- TechniqueStatus: not_evaluated, in_progress, validated, partial, etc.
- TestState: draft, in_review, validated, rejected
- TestResult: detected, not_detected, partially_detected

Services:
- audit_service.py: log_action() helper for audit logging

All models include proper foreign key relationships and PostgreSQL
enum types are managed correctly in migrations (create/drop).

backend/alembic/versions/14c6f07b47cb_add_tests_table.py

@@ -0,0 +1,57 @@
+"""add_tests_table
+
+Revision ID: 14c6f07b47cb
+Revises: 476930a8d86e
+Create Date: 2026-02-06 11:01:01.822240
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = '14c6f07b47cb'
+down_revision: Union[str, Sequence[str], None] = '476930a8d86e'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # Create enum types
+    testresult_enum = postgresql.ENUM('detected', 'not_detected', 'partially_detected', name='testresult')
+    teststate_enum = postgresql.ENUM('draft', 'in_review', 'validated', 'rejected', name='teststate')
+    testresult_enum.create(op.get_bind(), checkfirst=True)
+    teststate_enum.create(op.get_bind(), checkfirst=True)
+    
+    # Create table
+    op.create_table('tests',
+    sa.Column('id', sa.UUID(), nullable=False),
+    sa.Column('technique_id', sa.UUID(), nullable=False),
+    sa.Column('name', sa.String(), nullable=False),
+    sa.Column('description', sa.Text(), nullable=True),
+    sa.Column('platform', sa.String(), nullable=True),
+    sa.Column('procedure_text', sa.Text(), nullable=True),
+    sa.Column('tool_used', sa.String(), nullable=True),
+    sa.Column('execution_date', sa.DateTime(), nullable=True),
+    sa.Column('created_by', sa.UUID(), nullable=True),
+    sa.Column('result', postgresql.ENUM('detected', 'not_detected', 'partially_detected', name='testresult', create_type=False), nullable=True),
+    sa.Column('state', postgresql.ENUM('draft', 'in_review', 'validated', 'rejected', name='teststate', create_type=False), nullable=True),
+    sa.Column('validated_by', sa.UUID(), nullable=True),
+    sa.Column('validated_at', sa.DateTime(), nullable=True),
+    sa.Column('created_at', sa.DateTime(), nullable=True),
+    sa.ForeignKeyConstraint(['created_by'], ['users.id'], ),
+    sa.ForeignKeyConstraint(['technique_id'], ['techniques.id'], ),
+    sa.ForeignKeyConstraint(['validated_by'], ['users.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_table('tests')
+    # Drop enum types
+    postgresql.ENUM(name='testresult').drop(op.get_bind(), checkfirst=True)
+    postgresql.ENUM(name='teststate').drop(op.get_bind(), checkfirst=True)