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/ui.rs

@@ -63,6 +63,7 @@ fn render_modal(modal: &crate::app::Modal, theme: &Theme, frame: &mut Frame<'_>,
         Modal::RebuildConfirm(m) => render_rebuild_confirm(&m.summary, theme, frame, area),
         Modal::PathEntry(m) => render_path_entry(m, theme, frame, area),
         Modal::LoadPicker(m) => render_load_picker(m, theme, frame, area),
+        Modal::UndoConfirm(m) => render_undo_confirm(m, theme, frame, area),
     }
 }
 
@@ -316,6 +317,85 @@ fn render_rebuild_confirm(summary: &str, theme: &Theme, frame: &mut Frame<'_>, a
     frame.render_widget(paragraph, dialog_area);
 }
 
+/// `undo` / `redo` confirmation modal (ADR-0006 Amendment 1). Names
+/// the command that will be undone / re-applied and when its
+/// snapshot was taken, then prompts `Y` / `N`.
+fn render_undo_confirm(
+    m: &crate::app::UndoConfirmModal,
+    theme: &Theme,
+    frame: &mut Frame<'_>,
+    area: Rect,
+) {
+    let dialog_w = area.width.clamp(20, 60);
+    let inner_w = dialog_w.saturating_sub(4) as usize;
+
+    let intro = if m.is_redo {
+        crate::t!("modal.redo_confirm_command")
+    } else {
+        crate::t!("modal.undo_confirm_command")
+    };
+    let mut body_lines: Vec<String> = wrap_lines(&format!("{intro} {}", m.command), inner_w);
+    body_lines.extend(wrap_lines(
+        &crate::t!("modal.undo_confirm_when", timestamp = m.timestamp),
+        inner_w,
+    ));
+    let body_height = body_lines.len() as u16;
+    // Title row + blank + body + blank + prompt + blank + keys + borders (2).
+    let dialog_h = body_height.saturating_add(7).min(area.height);
+
+    let x = area.x + (area.width.saturating_sub(dialog_w)) / 2;
+    let y = area.y + (area.height.saturating_sub(dialog_h)) / 2;
+    let dialog_area = Rect {
+        x,
+        y,
+        width: dialog_w,
+        height: dialog_h,
+    };
+
+    frame.render_widget(ratatui::widgets::Clear, dialog_area);
+
+    let title = if m.is_redo {
+        crate::t!("modal.redo_confirm_title")
+    } else {
+        crate::t!("modal.undo_confirm_title")
+    };
+    let title_style = Style::default().fg(theme.fg).add_modifier(Modifier::BOLD);
+    let block = Block::default()
+        .borders(Borders::ALL)
+        .border_type(BorderType::Rounded)
+        .border_style(Style::default().fg(theme.fg))
+        .title(Line::from(vec![Span::styled(
+            format!(" {title} "),
+            title_style,
+        )]))
+        .style(Style::default().bg(theme.bg).fg(theme.fg));
+
+    let mut text_lines: Vec<Line<'_>> = Vec::new();
+    text_lines.push(Line::from(""));
+    for line in body_lines {
+        text_lines.push(Line::from(line));
+    }
+    text_lines.push(Line::from(""));
+    text_lines.push(Line::from(crate::t!("modal.undo_confirm_prompt")));
+    text_lines.push(Line::from(""));
+    text_lines.push(Line::from(vec![
+        Span::styled("[Y]", Style::default().fg(theme.fg).add_modifier(Modifier::BOLD)),
+        Span::raw(format!(" {}   ", crate::t!("shortcut.yes"))),
+        Span::styled("[N]", Style::default().fg(theme.fg).add_modifier(Modifier::BOLD)),
+        Span::raw(format!(" {}   ", crate::t!("shortcut.no"))),
+        Span::styled("Esc", Style::default().fg(theme.muted)),
+        Span::styled(
+            format!(" {}", crate::t!("shortcut.cancel")),
+            Style::default().fg(theme.muted),
+        ),
+    ]));
+
+    let paragraph = Paragraph::new(text_lines)
+        .block(block)
+        .wrap(Wrap { trim: false });
+    frame.render_widget(paragraph, dialog_area);
+}
+
 /// Greedy word-wrap to `width` columns. Sufficient for the
 /// short prose modals carry; we don't try to be Unicode-aware
 /// (display-width-wise) since the strings we generate are