feat(frontend): add recently added discovery rail

[apantaz]

Summary

• Add the filter-reactive Recently Added discovery rail
• Use provider addition dates independently from content release dates
• Extract a reusable catalog rail for lifecycle discovery sections
• Reuse cinematic cards with TMDB and verified provider links
• Add loading, empty, error, and retry states
• Update the README, frontend guide, and v0.5 roadmap

Validation

• 17 frontend tests passed
• Frontend lint and production build passed
• Full pre-commit and pre-push hooks passed
• dbt compile, parse, and documentation checks passed
• Offline test suite with coverage passed