feat: add floating and docked searchable file picker

src/main.rs

@@ -10,6 +10,8 @@ Default keys (configurable with config.bind):
 All modes: Ctrl+p command palette; type to filter, Up/Down select, Enter accept, Esc cancel
 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 picker; Space e docked explorer (right by default)
+       type to filter, Up/Down select, Enter opens, Esc returns, Ctrl+w closes, Ctrl+r refreshes
 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