feat: add literal buffer search and match navigation

src/main.rs

@@ -9,8 +9,9 @@ Usage: vamp [--config PATH | --no-config] [FILE]
 Default keys (configurable with config.bind):
 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
-        u undo, U redo, : command
+        u undo, U redo, : command, / search, n/N next/previous match
 Insert: Esc returns to normal
+Search: Enter finds next literal match, Esc cancels (case-sensitive, wraps)
 Commands: :w [PATH], :q, :q!, :wq [PATH], :plugins, :PLUGIN [ARGS]
 
 Ruby config: $XDG_CONFIG_HOME/vamp/config.rb or ~/.config/vamp/config.rb