Add comprehensive .gitignore and security workflows

[Copilot]

Enhance repository hygiene and security posture with comprehensive ignore patterns and automated vulnerability scanning.

.gitignore Enhancement (+136 patterns)

Added ignore patterns for modern JavaScript/TypeScript development:

• Test & Build: Playwright results, test coverage, build caches (Turbo, SWC, ESLint, TypeScript)
• Frameworks: Next.js artifacts, Vercel deployments, Yarn Berry PnP
• Platforms: Comprehensive macOS, Windows, Linux temporary files
• Tooling: IDE caches, editor backups, runtime data, debug logs

New Workflows

Dependency Review (dependency-review.yml)

Scans dependency changes in PRs for:

• CVE vulnerabilities (fails on high/critical)
• License compliance (MIT, Apache-2.0, BSD, ISC)
• Adds PR comments on findings

CodeQL Analysis (codeql.yml)

JavaScript/TypeScript security analysis with security-and-quality query suite:

• Runs on push, PRs, weekly schedule
• Integrates with GitHub Security tab
• Uses latest CodeQL v3 actions

Documentation

Updated WORKFLOWS_BEST_PRACTICES.md with new workflow descriptions and maintained existing best practices guidelines.

All workflows follow GitHub Actions standards: v4 actions, least-privilege permissions, concurrency control, appropriate timeouts, dependency caching.

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