feat: prepare server 1.2.0

[Priveetee]

Summary

• promote the Android YouTube playback contract with complete VOD DASH manifests and same-origin subtitle delivery
• reuse SABR playback sessions across same-format seeks and preserve generation isolation
• improve live SABR continuity, format selection and bounded buffering
• load subscription feeds progressively and recover expired YouTube extraction sessions

Production behavior

• Android clients can discover contract version 2 and prepare completed YouTube VODs with stable subtitle identities
• manual and auto-generated captions are delivered as session-scoped UTF-8 WebVTT
• active Android livestream playback remains explicitly unsupported
• no database migration or environment change is required

Runtime verification

• beta revision c96e38cb66a14cbad449bd5185a3d82c019898d6
• beta image ghcr.io/typetype-video/typetype-server-beta@sha256:fe8d9d87c20ab96e7f01fac1282e5e98fe78ca3f408267ff22f9b978876f0345
• validated Android VOD playback, complete DASH manifests, seek generations and same-origin subtitles
• validated VOD, SponsorBlock seeks, livestream playback and codec changes through the existing web player
• validated guest and authenticated subtitle isolation, stale generations and session expiry

Tests

• ./gradlew --no-daemon test
• ./gradlew --no-daemon check
• ./gradlew --no-daemon shadowJar
• git diff --check
• CI, OpenAPI and Docker workflows

Rollback

• previous stable Server image: ghcr.io/typetype-video/typetype-server@sha256:02053cbd467decdf7ca07beee0338a04457a0949e932d681641b76a0d3a3f2e3