feat: Add SponsorBlock integration and Dual Subtitles support

[Eliaway]

SponsorBlock:

• Full SponsorBlock API integration with privacy-preserving hash-based lookups
• Configurable categories (sponsor, selfpromo, interaction, intro, outro, filler, etc.)
• Auto-skip and manual skip button modes
• Merged with existing IntroDb/AniSkip skip intervals (deduplication via overlap detection)
• Per-platform SHA-256 implementations (Android/iOS/Desktop)
• Settings UI with category toggles and privacy mode

Dual Subtitles:

• Cross-platform SRT/WebVTT subtitle parser with binary search for O(log n) cue lookup
• Secondary subtitle rendered as Compose overlay (zero interference with native player)
• DualSubtitleSelector UI for picking secondary language from addon subtitles
• Customizable secondary subtitle style (color, size, position)
• Position-synced updates via existing playback snapshot pipeline

Modified files:

• PlayerScreenRuntimeEffects.kt: SponsorBlock fetch + merge + dual subtitle position updates
• PlayerPlaybackOverlays.kt: DualSubtitleOverlay placement
• SkipIntroButton.kt: Added SponsorBlock category labels

Summary

PR type

• Reproducible bug fix
• UI glitch/bug fix
• Behavior bug/regression fix
• Small maintenance only, with no UI or behavior change
• Docs accuracy fix
• Translation/localization only
• Approved larger or directional change

Why

Issue or approval

UI / behavior impact

• No UI change
• No behavior change
• UI changed only to fix a documented glitch/bug
• Behavior changed only to fix a documented bug/regression
• UI change has explicit maintainer approval
• Behavior change has explicit maintainer approval

Policy check

• I have read and understood CONTRIBUTING.md.
• This PR is small, focused, and limited to one problem.
• This PR is not cosmetic-only.
• Any UI change fixes a linked glitch/bug and includes visual proof, or this PR has no UI change.
• Any behavior change fixes a linked bug/regression or has explicit approval, or this PR has no behavior change.
• This PR does not bundle unrelated refactors, cleanups, formatting, or drive-by changes.
• This PR does not add dependencies, architecture changes, migrations, or product-direction changes without explicit approval.
• I listed the testing performed below.

UI polish, cosmetic-only changes, minor behavior tweaks, and unapproved product changes will be closed without review.

Scope boundaries

Testing

Screenshots / Video (UI changes only)

Breaking changes

Linked issues