Add security enhancements: linting infrastructure and ReDoS prevention

[cjcsecurity]

• Add ESLint with security plugins (eslint-plugin-security, eslint-plugin-no-unsanitized)
• Add package.json with linting dependencies (ESLint, web-ext)
• Add automated lint workflow for CI/CD
• Update .gitignore to exclude package-lock.json and web-ext-artifacts
• Fix ReDoS vulnerabilities in regex patterns (IPv4, IPv6, domain validation)
• Prevent object injection by using explicit color mapping
• Remove unused variable to clean up code

[cjcsecurity]

The failing web-ext lint test is reporting Firefox compatibility issues (MANIFEST_FIELD_UNSUPPORTED for service_worker) which is expected since this is a Chrome-only extension using Manifest V3 syntax. All security checks pass (CodeQL, dependency review, npm audit, ESLint) and the code quality improvements in this PR are valuable - adding ESLint security plugins, fixing ReDoS vulnerabilities, and implementing automated linting. The tabGroups API warnings are also Firefox-related and the code already has proper fallback handling. Safe to merge as the lint failure is purely about Firefox compatibility for a Chrome-only extension, not a code quality or security issue.