Created Lint check CI action

[Adithyan-Dinesh-Trenser]

Add ESLint CI Lint Check

Introduces a GitHub Actions workflow that runs ESLint on every push and PR, scoped to only the lines changed in each push — so existing lint debt doesn't block new work.

What's included

.github/workflows/lint.yml

• Triggers on all branch pushes and on PRs targeting nightly / production
• Uses eslint-plugin-diff to lint only changed lines (not the entire codebase)
• Handles edge cases: new branches, force pushes, and rebases by falling back to HEAD~1 when the before commit is unavailable
• Installs lint dependencies directly via npm install --no-save (no package.json changes required)
• Deduplicates @typescript-eslint plugin to avoid conflicts with eslint-config-react-app

.eslintrc.json

• Copied from Viewer
• Base ESLint config shared between local development and CI
• Extends react-app, eslint:recommended, @typescript-eslint/recommended, and prettier
• Enforces curly (brace style) as an error; disables import/no-anonymous-default-export
• Registers Cypress globals to suppress false positives in test files

Test plan

• Push a branch with a lint error on a changed line — workflow should fail
• Push a branch with clean changes — workflow should pass
• Open a PR to nightly or production — lint runs against the PR base SHA