feat: bind Ctrl-U to backward line deletion

src/main.rs

@@ -38,6 +38,7 @@ Insert: Ctrl+n requests LSP completion at primary caret, then cycles next; Ctrl+
         Candidates replace text live; Original text restores it; other keys close and act normally
         Snippets expand fully: type replaces argument, Tab/Shift+Tab next/previous, final $0 ends
         Outside snippets Enter inserts newline, Tab inserts tab; Esc keeps text and returns to Normal
+Insert/Command/Search: Ctrl+u deletes backward to the logical line start
 Search: Enter finds next literal match, Esc cancels (case-sensitive, wraps)
 Commands: :save [PATH], :quit, :force_quit, :save_and_quit [PATH], :plugins, :PLUGIN [ARGS]
 Aliases: w=save, q=quit, q!=force_quit, wq=save_and_quit