chore(ci): make lint checks non-mutating

[TheRealAgentK]

Summary

• make npm run eslint and npm run tseslint check-only instead of silently modifying files in CI
• add explicit eslint:fix and tseslint:fix scripts for intentional local fixes
• disable @stylistic/indent-binary-ops, which conflicts with Prettier's formatting of TypeScript union types

Motivation

After the development-tool refresh, npm run tseslint exited successfully while changing lib/raygun.ts; that ESLint-produced change then failed Prettier. CI did not catch the inconsistency because lint and formatting run in separate workspaces and the lint scripts used --fix.

Prettier remains the formatting authority, while ESLint now performs non-mutating static analysis in CI.

Verification

• npm ci
• npm run eslint — passed without changing tracked files
• npm run tseslint — passed without changing tracked files
• npm run eslint:fix — passed
• npm run tseslint:fix — passed without conflicting with Prettier
• repository Prettier check
• npm test — 258 tests passed
• npm run test:cjs
• npm audit — 0 vulnerabilities
• git diff --check

[Olwiba]

lgtm :)