fix: album art repaint, idle reconnect, greyscale themes

[odiumuniverse]

• Blank and overdraw the album art with CellDiffOption::AlwaysUpdate; ratatui-image marks the image's cells Skip without changing their symbols, and a blank cell compares equal to the blank already there, so Clear over an image wrote nothing and the picture survived every attempt to erase it
• Draw overlays on top of the cover instead of under it — the actions menu used to leave its right-hand half stencilled across the art with the image gone
• Write the image escape only when the cover actually changes; it went out on every frame, so a recolour that repaints the screen dozens of times in a row made the cover flicker
• Rebuild the session, player and Connect device when the access point stops answering; librespot invalidates the session on a keep-alive timeout and leaves recovery to the caller (session.rs: "TODO: Optionally reconnect"), so every command afterwards failed with Internal error { channel closed } until a restart
• Take the theme's base hue from the most saturated swatch, not the dominant one; rgb_to_hsl reports hue 0 for every grey and hue 0 is red, so black-and-white covers all painted the UI the same burgundy
• Scale the surface tint by how colourful the art is, so greyscale art gets a neutral UI instead of an arbitrary hue, and stop for_dark_fg raising saturation on an achromatic swatch
• Present each frame atomically with synchronized output (DECSET 2026); a track change recolours every glyph at once and the terminal rendered that half-applied
• Run the theme cross-fade over 1200ms instead of 300ms — smoothness comes from duration, since every present recomposes the viewport
• Drop the blind two-second art resend under tmux; it re-encoded the cover to produce an identical cell the diff discarded, so it never recovered anything
• Honour protocol and MYX_PROTOCOL inside a sixel-capable tmux; the sixel picker drops tmux passthrough, so a forced kitty or iTerm2 left its escapes for tmux to eat
• Detect kitty from the client tmux has attached now instead of KITTY_WINDOW_ID, which lingers in a session's environment after reattaching from another terminal
• Build the picker before the tokio runtime and the player exist — picking sixel swaps TERM around the query, and setenv is only safe without concurrent readers
• Ignore the keys that only drive the hidden library in zen mode, and drop their footer hints; a retargets onto the playing track rather than the invisible selection
• Give each cache write a unique temp name so two threads fetching the same URL can't interleave into one corrupt entry