feat: add counted forward and backward character seek motions

src/main.rs

@@ -17,6 +17,7 @@ Files: Space o floating tree INSERT; Space e docked tree NORMAL (right by defaul
 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
+        Normal/Visual: f<char>/F<char> seek next/previous on current line; 2fx seeks second x
         gf follows Markdown file links/reference links and heading fragments (no LSP)
         Normal/Visual: gt first line, gb last line, at first nonblank; Esc cancels g
         Ctrl+o older jump location; Ctrl+i/Tab newer (counts supported)