release 0.2.1: merge dev to main

[threehappypenguins]

VideoSphere 0.2.1

YouTube import

• Faster, more reliable downloads — imports now fetch the full source with parallel fragments and tuned HTTP chunking, then trim with ffmpeg instead of using --download-sections.
• Smoother progress — download progress accounts for separate video and audio streams so the bar no longer jumps when the second stream starts.
• Better audio compatibility — prefers AAC/m4a audio when merging so imported files stay closer to the source format.

YouTube trim editor

• Finer trim controls — frame-step buttons, configurable jump steps (e.g. 5s / 10s), and click-to-edit timestamps (0:10, 1:30, 1:02:03).
• Keyframe snapping — snapping runs from the new frame-step controls; keyboard/drag behavior is unchanged for preview seeking.

Mobile UX

• Responsive modal footers — draft and livestream metadata modals use a stacked mobile layout on narrow screens.
• Hydration fix — viewport detection defaults to the mobile layout during SSR/first paint to avoid layout flicker on small screens.

Livestreams

• Delete from the edit modal — remove drafts or livestreams directly from the metadata modal, with a confirmation step.
• Shared delete helper — livestream deletion logic is centralized for consistent API calls and toast feedback.

Fixes

• Trim timestamp inputs no longer commit twice on blur after pressing Enter.