feat(frontend): add shared global filters

[apantaz]

Summary

Adds the shared global-filter experience used by every WatchPulse discovery section.

Changes

• Adds content type, genre, runtime, release-year, rating, and language filters
• Loads filter options from the scoped local catalog
• Persists validated guest preferences in browser-local storage
• Adds safe FastAPI query-parameter serialization
• Handles invalid saved values and reversed year ranges
• Adds responsive controls and clear-filter behavior
• Updates frontend documentation and the v0.5 roadmap

Validation

• 9 frontend tests pass
• ESLint and strict TypeScript checks pass
• Production frontend build passes
• Pre-commit and pre-push hooks pass