feat(youtube): skip sponsors in the TV interface#8

Summary

• add an optional original MIT MV3 companion for YouTube TV watch routes, informed by TizenTube's native-video/hash-route approach
• request only sponsor/skip segments from the fixed SponsorBlock API using a four-character SHA256 hash bucket, without credentials, referrers, submissions or viewed-segment reports
• follow route/video replacement, pause, seek and playback rate; stale responses, unloaded media, known ads and mismatched duration cannot seek

Stacking

feat/browser-extensions ← feat/youtube-tv-sponsorblock. Depends on #7 (optional loader) and #6 (mandatory profiles); merge after #1 → #2 → #3 → #4 → #5 → #6 → #7. Enable through the existing optional loader by mounting extensions/tv-sponsorblock read-only. This retains YouTube's TV interface and adds no Cast/DIAL/VPN endpoint or browser preview.

Verification

• 11 focused tests cover the worker's source/URL/ID/segment policy and content-script request generations, timers, ad/duration gating, replaced videos, route cleanup and refused seeks
• real Chromium 154 with unmodified companion and real SponsorBlock API: YouTube TV guest playback allowed two 15.041 s prerolls, then automatically sought to 869.757, 880.707 and 893.842 across three community sponsor segments
• isolated HTTPS/native-video fixture verified pause/resume, ad gating and route-away cleanup; no production API overrides or injected segment data
• npm test: final full stack: 163/163 on macOS and Fedora/Node 22; JavaScript syntax and git diff --check pass
• direct Opus 5.5 High review on NB-LVLQYQ1F3D: no findings at e4c0e9237ea81fe4ef3afa18f6eff74ab8c4bab3

Limits and attribution

Only the sponsor category is implemented. Unknown/stale duration, live media and API failures leave playback alone. Undocumented TV-player changes or equal-duration ads can evade DOM/duration checks. SponsorBlock sees the server IP/hash bucket; hashing is not anonymity. The README credits SponsorBlock data under CC BY-NC-SA 4.0 and the pinned TizenTube source; no TizenTube code was copied. The live stream was left running.