Add CI for the extension (typecheck, lint, unit + e2e)

[aadityat23]

Category: DevOps / Extension · Difficulty: Beginner · Effort: Small · Priority: Core

Skills: GitHub Actions, npm workspaces, Playwright

Good for: DevOps Intern / SDE Intern

Description: finverify-extension/package.json already defines typecheck, lint, and presumably test scripts across the npm workspace, and there are 11 test files (including Playwright e2e under apps/extension/e2e) — but .github/workflows/ has no extension workflow at all.

Expected outcome: A extension-tests.yml workflow mirroring the structure of the existing backend-tests.yml/sdk-tests.yml.

Acceptance criteria:

• Workflow runs on PRs touching finverify-extension/**
• runs typecheck + lint + tests, is green on a clean checkout.

Files: .github/workflows/, finverify-extension/package.json

Labels: devops, extension, good first issue