feat: add editor tabs

src/main.rs

@@ -21,6 +21,8 @@ Normal: i/a insert, I/A insert at first nonblank/end, o/O new line
         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)
+        _ splits above/below, | left/right; Option/Alt+h/j/k/l focuses neighboring panes
+        Ctrl+Option/Alt+h/l previous/next tab; :tab.new opens current buffer in another tab
         Normal/Visual: prefix motions with counts (5j, 2w, 3n); Esc cancels count
         u undo, U redo, : command, / search, n/N next/previous match
         dd deletes lines; cc changes lines and enters Insert; counts: 3dd, 2cc; Esc cancels prefix
@@ -42,6 +44,8 @@ Aliases: w=save, q=quit, q!=force_quit, wq=save_and_quit
 Buffers: :edit PATH, :buffers, :buffer N, :buffer_next, :buffer_previous, :buffer_delete [N], :buffer_force_delete [N]
          Aliases: bnext, bprev, bdelete, bdelete!; arguments and safety rules are unchanged
          :quit refuses any dirty buffer; :save_and_quit saves active and quits only if all are clean
+Tabs: :tab.new, :tab.previous, :tab.next, :tab.close, :tab.force_close
+      Tabs retain pane layouts and independent views; close protects exclusively displayed unsaved edits
 Markdown links: :follow_link (primary caret; local files only)
 Diff: :diff (Normal); choose Before then After; Working checkout After edits live unsaved buffers
       Before and historical/remote After stay read-only; Tab/Shift+Tab categories/Normal focus