fix: make all icon buttons fully round (rounded-full)

Commit notes

Updated icon buttons across the app for consistent styling: - TransportControls: play/stop and reset buttons - SequencerTrack: delay, reverb, bitcrusher FX buttons - Header: library, sequencer, and notifications buttons - GainMeter: volume cycle button - GrooveControls: groove cycle button - KeyboardShortcuts: keyboard shortcuts trigger button - PackOrganizer: select all and clear selection buttons - LibrarySearchFilter: sort order toggle button - LibrarySampleGrid: edit sample button - SharePopover: share and copy link buttons - share/[token]/+page: download button - Toaster: close notification button

Co-authored-by: armin.naimi <[email redacted]>