Add E2E Tests for Alerts and Incidents Flows

[Johnpii1]

Description

Description
Add mocked incident fixtures and route handlers to e2e/utils/mockApi.ts to support /api/v1/incidents listing, filtering, and /:id/read acknowledgement.
Add Playwright page objects e2e/pages/AlertsPage.ts and e2e/pages/IncidentsPage.ts to encapsulate interactions for alerts and incident heatmap.
Add E2E spec e2e/tests/alerts-incidents.spec.ts that covers alert listing, severity/status/search filters, bulk triage actions (mark-read/dismiss), and incident heatmap cell assertions.
Closes #725.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that changes existing behaviour)
• Refactoring (no functional changes)
• Documentation update
• CI/CD change
• Dependency update

Related Issue

Closes #725

Changes Made

Testing

Testing
Built the frontend with npm --workspace=frontend run build which completed successfully.
Ran npm run test:e2e -- --project=chromium e2e/tests/alerts-incidents.spec.ts but the Playwright browser executable was not present so the tests failed to launch (error: missing Chromium executable).
Attempted npx playwright install chromium firefox to install browsers but the download failed (Playwright CDN returned 403 Forbidden), blocking E2E test execution.

• Unit tests pass locally (npm run test:unit)
• Integration tests pass locally (npm run test:integration)
• New tests added for new behaviour
• Manual testing completed — describe below if relevant

Manual test steps (if applicable):

Migration Changes

• No database migrations in this PR
• New migration file generated with npm run migrate:make
• Migration validated with npm run migrate:validate
• down() function tested locally
• No data loss in the rollback path

Documentation

• No documentation changes needed
• README.md updated (new commands, endpoints, or setup steps)
• Relevant docs/ file updated
• .env.example updated (new environment variables)
• Inline comments / JSDoc updated for changed functions
• backend/docs/API.md updated (new or changed endpoints)

Checklist

• Branch is up to date with main
• PR title follows Conventional Commits format (type(scope): summary)
• Code follows project style — linters pass (npm run lint, cargo clippy)
• Build succeeds (npm run build, cargo build --release)
• No console.log / println! left in production code
• No secrets, credentials, or .env files committed
• Self-review completed — I have read my own diff

CI Status

• Backend lint, build, and tests pass
• Frontend lint, build, and tests pass
• Contract format check, Clippy, and tests pass
• Security scan passes (no new vulnerabilities)
• Docker build succeeds

Screenshots

Breaking Changes

Additional Notes

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