feat: expand completion snippets and navigate placeholders

src/main.rs

@@ -19,7 +19,7 @@ Normal: i/a insert, I/A insert at first nonblank/end, o/O new line
         w/b/e word next/previous/end, W/B/E whitespace-delimited WORDs
         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; Insert Tab unchanged)
+        Ctrl+o older jump location; Ctrl+i/Tab newer (counts supported)
         Normal/Visual: prefix motions with counts (5j, 2w, 3n); Esc cancels count
         u undo, U redo, : command, / search, n/N next/previous match
         Normal/Visual: . repeats last native edit at current targets (one undo group)
@@ -32,7 +32,8 @@ Visual: motions extend selections, y copy, d/x/Delete cut, c change
         v/V switches selection shape; same selector or Esc cancels retaining carets
 Insert: Ctrl+n requests LSP completion at primary caret, then cycles next; Ctrl+j/k next/previous
         Candidates replace text live; Original text restores it; other keys close and act normally
-        Enter inserts newline, Tab inserts tab, Esc returns to Normal retaining candidate/carets
+        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
 Search: Enter finds next literal match, Esc cancels (case-sensitive, wraps)
 Commands: :w [PATH], :q, :q!, :wq [PATH], :plugins, :PLUGIN [ARGS]
 Buffers: :edit PATH, :buffers, :buffer N, :bnext, :bprev, :bdelete[!] [N]