feat: retain explorer filters in navigation mode

src/main.rs

@@ -12,7 +12,8 @@ Normal/Visual: Space is leader; Space Space opens palette; Esc cancels prefix
 Normal leader: Space w saves; Space b n/p/l/d next/previous/list/close buffer
 Files: Space o floating tree INSERT; Space e docked tree NORMAL (right by default)
        tree NORMAL: hjkl navigate; INSERT: type to filter, Ctrl+hjkl navigate; Enter toggles/opens
-       i filters in tree INSERT; Esc returns NORMAL, then editor; Ctrl+t view, Ctrl+w close, Ctrl+r refresh
+       i filters; Esc retains filter and returns NORMAL, then editor; Ctrl+u clears in either mode
+       Ctrl+t view, Ctrl+w close, Ctrl+r refresh
 Normal: i/a insert, I/A insert at first nonblank/end, o/O new line
         h/j/k/l move, 0/$ line ends, x delete, J join lines
         w/b/e word next/previous/end, W/B/E whitespace-delimited WORDs