feat: ADR-0006 §8 steps 4-5 — undo/redo commands + confirm-modal flow

Commands & grammar (step 4):
- AppCommand::Undo/Redo, grammar nodes + REGISTRY entries, catalog
  help/usage + keys; parse tests
- replay skips undo/redo (is_app_lifecycle_entry_word) + completion
  entry-keyword lockstep; replay-skip test extended

Wiring (step 5):
- Action::{PrepareUndo,PrepareRedo,Undo,Redo} + AppEvent::{UndoPrepared,
  UndoUnavailable,UndoSucceeded,UndoFailed}
- App: undo_enabled flag, Modal::UndoConfirm, dispatch + event handling
  + confirm-key handler (Y confirms / N/Esc cancels); "turned off" when
  --no-undo; "nothing to undo/redo" when empty
- ui::render_undo_confirm names the command + snapshot time
- runtime: opens with undo enabled (!--no-undo), threads it through the
  project-switch path, spawn_prepare_undo/spawn_undo (peek->modal,
  restore->refresh tables + schema cache)
- 9 Tier-1 app tests + 3 parse tests

1692 passed / 0 failed / 1 ignored; clippy clean.

src/friendly/keys.rs

@@ -168,6 +168,8 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("help.app.import", &[]),
     ("help.app.mode", &[]),
     ("help.app.messages", &[]),
+    ("help.app.undo", &[]),
+    ("help.app.redo", &[]),
     ("help.ddl.create", &[]),
     ("help.ddl.drop", &[]),
     ("help.ddl.add", &[]),
@@ -257,7 +259,9 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("parse.usage.new", &[]),
     ("parse.usage.quit", &[]),
     ("parse.usage.rebuild", &[]),
+    ("parse.usage.redo", &[]),
     ("parse.usage.replay", &[]),
+    ("parse.usage.undo", &[]),
     ("parse.usage.save", &[]),
     ("parse.usage.select", &[]),
     ("parse.usage.show_data", &[]),
@@ -353,6 +357,22 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("modal.rebuild_cancelled", &[]),
     ("modal.rebuild_confirm_prompt", &[]),
     ("modal.rebuild_confirm_title", &[]),
+    ("modal.redo_cancelled", &[]),
+    ("modal.redo_confirm_command", &[]),
+    ("modal.redo_confirm_title", &[]),
+    ("modal.undo_cancelled", &[]),
+    ("modal.undo_confirm_command", &[]),
+    ("modal.undo_confirm_prompt", &[]),
+    ("modal.undo_confirm_title", &[]),
+    ("modal.undo_confirm_when", &["timestamp"]),
+    // ---- Undo / redo command surfaces (ADR-0006 Amendment 1) ----
+    ("undo.disabled", &[]),
+    ("undo.nothing_to_undo", &[]),
+    ("undo.nothing_to_redo", &[]),
+    ("undo.undone_ok", &["command"]),
+    ("undo.redone_ok", &["command"]),
+    ("undo.undo_failed", &["error"]),
+    ("undo.redo_failed", &["error"]),
     // ---- Status bar + panels ----
     ("panel.hint_empty", &[]),
     ("panel.hint_title", &[]),