fix: media deck / mini player state, YouTube handoff, controls

[kwalus]

Summary

• Media deck vs mini player: deferred YouTube materialize, mini/deck switching, forceDockMini on minimize, source launchers.
• YouTube handoff across hosts (post/sidebar) with prepare/skip URL for mini↔deck; player bridge reset when src changes.
• State repair: repairMediaCurrentReference, reconcileDeckStageMediaPlacement, safer updateMini/updateDeckPanel.
• Deck UI: header wrap, sticky footer Collapse + Mini bar, portal layout unchanged.
• Frontend regression tests + CHANGELOG [Unreleased].

Also includes any pending version/docs edits already in the working tree (pyproject, canopy/init, README, docs).