Finalize ConspiracyAlert extension artifact

[VincenzoImp]

Summary

• Add the maintained ConspiracyAlert Chrome/Chromium extension client for the Channel Checker backend.
• Implement popup checks, automatic page checks, in-page warnings, backend settings, and per-tab badge state.
• Add generated API types, CI, packaging, artifact documentation, citation metadata, license, and tests.

Validation

• npm ci
• npm run check
• npm test (21 passed)
• npm audit --audit-level=moderate
• npm run build
• npm run check:api-types
• npm run package
• npm run test:e2e (2 passed)

Notes

Local setup and reviewer instructions are documented in ARTIFACT.md.