0.5.2

feat: bound the editor push debounce at two seconds

A trailing debounce that resets on every keystroke never fires during
continuous typing: work stayed unsynced and invisible to other devices
for as long as the author kept writing (measured: 24 s of typing, zero
pushes). The debounce is now min(delay, remaining burst window) with a
two-second cap since the first unsynced edit.

Default sync delay drops 700 -> 300 ms and the slider floor 300 -> 100 ms;
transport measures ~118 ms one-way and external file changes already
bypass the debounce entirely.