feat: follow Markdown file links and heading fragments

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
+        gf follows Markdown file links/reference links and heading fragments (no LSP)
         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)
@@ -32,6 +33,7 @@ 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]
          :q refuses any dirty buffer; :wq saves active and quits only if all are clean
+Markdown links: :follow_link (primary caret; local files only)
 
 Ruby config: $XDG_CONFIG_HOME/vamp/config.rb or ~/.config/vamp/config.rb
 Set VAMP_RUBY to choose the Ruby executable.