feat(editor): rename :sync to :gp

Pairs with :gl as the push half of the git pair. Same behavior
(fmt → save → commit → push); notices, logs, and current READMEs
follow, historical docs keep :sync as a record of their time.

display/src/lib.rs

@@ -47,7 +47,7 @@ impl Frame {
 
     /// Reset to all-white paper, reusing the existing allocation when the
     /// buffer is already full-size. This is what lets firmware repaint without
-    /// allocating: a background `:sync` push can take the heap to the floor,
+    /// allocating: a background `:gp` push can take the heap to the floor,
     /// and a failed framebuffer alloc aborts the whole app (2026-07-13).
     pub fn clear_white(&mut self) {
         self.buf.clear();