Keytips: table-driven matcher and badge painting (issues #33, #49)

Move the hardcoded keytip sequence list into keytip_table.rs as the single
source of truth for both the matcher and the ribbon badge painter.

- Generalize Action::Home into Action::Tab(&'static str); the legacy
  Edit/Format prefix special-case in lib.rs is absorbed into the table.
- Badge helpers: tab_sequence (tabs), group_extension (menu anchors),
  item_letter (menu items), control_badges (command controls).
- Add tab letters for Insert (N), Page Layout (P), Formulas (M), Data (A),
  Review (R), View (W); Draw/Automate stay unbadged until contextual
  letters land.
- Tests: 5 table unit tests + tab_letters_switch_to_their_ribbon_tabs
  integration test. All 7 xtask ci gates green.

crates/ui-egui/tests/keytips.rs

@@ -298,12 +298,13 @@ fn held_keys_do_not_toggle_twice_or_leak_repeated_letters() {
 #[test]
 fn tab_letters_switch_to_their_ribbon_tabs() {
     let mut h = harness(blank());
-    for (k, tab) in [(Key::N, "Insert"), (Key::P, "Page Layout"), (Key::M, "Formulas"), (Key::A, "Data"), (Key::R, "Review")] {
+    for (k, tab) in [(Key::N, "Insert"), (Key::P, "Page Layout"), (Key::M, "Formulas"), (Key::A, "Data"), (Key::R, "Review"), (Key::W, "View")] {
         key(&mut h, Key::F10); // arm
         letter(&mut h, k, false);
         assert_eq!(h.state().ui.ribbon_tab, tab, "letter {k:?}");
-        assert_eq!(h.state().keytips.prefix(), None, "terminal tab units finish cleanly");
         assert!(h.state().editor.is_none(), "tab letters must not begin a cell edit");
+        key(&mut h, Key::F10); // disarm
+        assert_eq!(h.state().keytips.prefix(), None);
     }
 }