feat(frontend): add region and provider selection

[apantaz]

Summary

Adds API-driven region and streaming-provider selection to the v0.5 frontend.

Changes

• Loads available regions from the WatchPulse API
• Displays localized region names with ISO codes
• Loads region-aware streaming providers
• Supports selecting multiple providers
• Removes invalid provider selections after changing region
• Persists valid guest preferences in browser-local storage
• Adds responsive loading and error states
• Updates the frontend documentation and v0.5 roadmap

Validation

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