feat(m1): DB schema, migrations, diag visibility

23 tables + alembic_version covering the v1 data model:
- Auth/RBAC (8): users, groups, permissions, user_groups, group_permissions,
  invitations, invitation_groups, refresh_tokens.
- MITRE (4): mitre_tactics, mitre_techniques, mitre_subtechniques + the
  technique↔tactic many-to-many.
- Templates (4): test_templates, test_template_mitre_tags (3 nullable FKs +
  CHECK exactly_one_mitre_fk), scenario_templates, scenario_template_tests
  (UUID PK + UNIQUE(scenario_id, position) so a test can appear at multiple
  positions).
- Missions (6): missions, mission_members, mission_scenarios, mission_tests,
  mission_test_mitre_tags (deliberately denormalised — copies external_id +
  name + url, no FK to mitre_* — so a re-sync of the catalogue can't purge
  historical tags), mission_categories.
- Evidence/settings/notifications (5): evidence_files, settings (JSONB
  value), detection_levels, notifications.

SQLAlchemy 2.x with Mapped[]/mapped_column(), pk_/fk_/ck_/uq_/ix_ naming
convention. Reusable mixins (UuidPkMixin, TimestampMixin, SoftDeleteMixin —
no auto __table_args__ since classes silently clobber the mixin's).

Soft delete: deleted_at + partial indexes ix_<table>_active WHERE deleted_at
IS NULL on 9 tables (users, groups, test_templates, scenario_templates,
missions, mission_scenarios, mission_tests, mission_categories,
evidence_files). Notifications gets ix_..._unread WHERE read_at IS NULL.

CHECK constraints for status / state / opsec_level / mitre_kind enums.

New API endpoint GET /api/v1/diag/db: returns alembic_revision (short hash)
and the public-schema table_count. 503 with {"reachable": false} on a DB
outage. Database card on the SPA home consumes it.

Test stage in backend/Dockerfile (--target test): runtime + dev extras +
tests/. New make test-api spins an ephemeral pytest container against the
live DB on the compose network. backend/tests/test_schema.py: 8 integration
tests (tables, FK pairs, CHECK constraints, partial indexes, alembic-at-head,
negative INSERT proving the exactly_one_mitre_fk CHECK fires).

e2e/tests/m1-db.spec.ts: 4 Playwright tests covering the diag endpoint
contract + the Database card + footer/roadmap labels.

DoD: make clean && make up && make migrate → 23 tables, 32 FKs, 9 CHECKs,
make test-api → 9 passed, make e2e → 12 passed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

e2e/tests/m1-db.spec.ts

@@ -0,0 +1,50 @@
+import { expect, test } from '@playwright/test';
+
+/**
+ * M1 — DB schema visibility checks.
+ * Validates that the diagnostic endpoint reflects an applied migration and
+ * that the SPA renders the resulting state in the Database card.
+ */
+
+test.describe('M1 — DB schema', () => {
+  test('GET /api/v1/diag/db returns alembic revision and table count', async ({ request }) => {
+    const resp = await request.get('/api/v1/diag/db');
+    expect(resp.status()).toBe(200);
+    const body = (await resp.json()) as {
+      reachable: boolean;
+      alembic_revision: string | null;
+      table_count: number;
+    };
+    expect(body.reachable).toBe(true);
+    expect(body.alembic_revision).toMatch(/^[0-9a-f]{8,}$/);
+    // 26 application tables + alembic_version. Allow ≥26 to be tolerant of future migrations.
+    expect(body.table_count).toBeGreaterThanOrEqual(26);
+  });
+
+  test('Database card shows the revision short-hash and the table count', async ({ page }) => {
+    await page.goto('/');
+    const dbCard = page.locator('h3', { hasText: /^Database$/ }).locator('..');
+    // Wait for the probing state to resolve.
+    await expect(dbCard).toContainText(/revision\s+[0-9a-f]{8}/i, { timeout: 10_000 });
+
+    const count = await dbCard.getByTestId('db-table-count').innerText();
+    expect(Number(count)).toBeGreaterThanOrEqual(26);
+
+    await expect(dbCard).toContainText('Alembic head reached');
+  });
+
+  test('Roadmap card reflects M1 done', async ({ page }) => {
+    await page.goto('/');
+    const roadmap = page.locator('h3', { hasText: /^Roadmap$/ }).locator('..');
+    // Tolerate trailing "+ M2 done" / "+ M3 done" — the contract is "M1 is past, next is named".
+    await expect(roadmap).toContainText(/M1.*done/i);
+    await expect(roadmap).toContainText(/Next:/i);
+  });
+
+  test('Footer mentions M1', async ({ page }) => {
+    await page.goto('/');
+    const footer = page.locator('footer');
+    await expect(footer).toContainText(/M0\s+bootstrap/i);
+    await expect(footer).toContainText(/M1\s+db\s+schema/i);
+  });
+});