fix: prepare frontend 1.2.1

[Priveetee]

Summary

• update the MSE runtime to 0.1.42
• stabilize SABR seeks and mobile browser lifecycle recovery
• preserve the active player and playback speed across temporary transitions
• improve mobile landscape playback and touch-based history removal
• align the Frontend version with TypeType 1.2.1

Production behavior

• Safari and iOS no longer revive an obsolete playback loop after SponsorBlock seeks
• buffered and repeated seeks preserve the active playback session when possible
• fullscreen, Picture-in-Picture, orientation and background transitions preserve media state
• metadata enrichment no longer replaces the active SABR player
• no environment change is required

Runtime verification

• beta behavior revision 9c82a4c15ced3ac880be0f7dd4b1bb29d53d081f
• @typetype/mse@0.1.42 is published and pinned
• validated SponsorBlock, repeated seeks, background recovery, fullscreen and orientation changes
• validated Safari/WebKit and Chromium-based mobile PWA playback
• version-only release commit 3658b7de2217bcdf85cde54c4a81f0a20a7e041c

Tests

• Frontend Coverage and Docker workflows
• Player CI for dcd3bf4cc6f414d208bb741b5694b8a0519a9301
• git diff --check

Rollback

• previous stable Frontend revision: 30858e7855a75629f5e5f828ee00b49497d902d6
• previous stable image remains available by immutable digest