feat(L+M): configurable dashboard widget system + test framework

Phase L: Dashboard widget system
- Migration 046: dashboard_configs table (user/tenant/role fallback cascade)
- DashboardConfig model + dashboard_service with get/upsert per-user and tenant-default
- API router: GET/PUT /api/dashboard/config, GET/PUT /api/dashboard/tenant-default
- Frontend: 5 widget components (ProductionStats, QueueStatus, RecentRenders, CostOverview, WorkerStatus)
- DashboardGrid with API-backed config, DashboardCustomizeModal (checkbox selection, save/cancel)
- Dashboard.tsx: widget grid + analytics section (privileged users)
- Admin.tsx: restructured with new section order and Maintenance 2-col grid

Phase M: Test framework
- Backend: pytest-asyncio + pytest-cov + factory-boy in pyproject.toml
- conftest.py: excel_dir fixtures + async DB fixtures + mock storage/celery stubs
- Domain tests: billing_service, cache_service, notifications_service, imports_sanity
- Integration: test_api_health.py smoke test (requires running backend)
- Frontend: vitest + @testing-library/react + msw added to package.json
- vite.config.ts: test block (jsdom + globals + setupFiles)
- tsconfig.json: exclude src/__tests__ from main tsc (test runner handles its own types)
- MSW handlers for /api/auth/me, Billing.test.tsx, formatters.test.ts

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

backend/alembic/versions/046_dashboard_configs.py

@@ -0,0 +1,48 @@
+"""Add dashboard_configs table.
+
+Revision ID: 046
+Revises: 045
+"""
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+revision = '046'
+down_revision = '045'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_table(
+        'dashboard_configs',
+        sa.Column('id', UUID(as_uuid=True), primary_key=True, server_default=sa.text('gen_random_uuid()')),
+        sa.Column('tenant_id', UUID(as_uuid=True), sa.ForeignKey('tenants.id', ondelete='CASCADE'), nullable=True),
+        sa.Column('user_id', UUID(as_uuid=True), sa.ForeignKey('users.id', ondelete='CASCADE'), nullable=True),
+        sa.Column('widgets', JSONB, nullable=False, server_default=sa.text("'[]'::jsonb")),
+        sa.Column('is_tenant_default', sa.Boolean, nullable=False, server_default='false'),
+        sa.Column('created_at', sa.DateTime, nullable=False, server_default=sa.text('NOW()')),
+        sa.Column('updated_at', sa.DateTime, nullable=False, server_default=sa.text('NOW()')),
+    )
+    # Unique: one config per user
+    op.create_index(
+        'uq_dashboard_config_user',
+        'dashboard_configs',
+        ['user_id'],
+        unique=True,
+        postgresql_where=sa.text('user_id IS NOT NULL'),
+    )
+    # Unique: one tenant-default per tenant
+    op.create_index(
+        'uq_dashboard_config_tenant_default',
+        'dashboard_configs',
+        ['tenant_id'],
+        unique=True,
+        postgresql_where=sa.text('is_tenant_default = true'),
+    )
+
+
+def downgrade():
+    op.drop_index('uq_dashboard_config_tenant_default', table_name='dashboard_configs')
+    op.drop_index('uq_dashboard_config_user', table_name='dashboard_configs')
+    op.drop_table('dashboard_configs')