Iteration 4a: rebuild command with confirmation modal

Adds the explicit `rebuild` app-level command (ADR-0015 §7, §11)
and a modal UI infrastructure to host its confirmation dialog.
Typing `rebuild` emits Action::PrepareRebuild; the runtime reads
project.yaml + data/ to compute a summary ("3 tables and 47 rows
will be reconstructed; the existing playground.db will be
replaced") and posts AppEvent::RebuildPrepared, which opens the
modal. Y confirms, N/Esc cancels. While the modal is open,
normal input is gated.

The worker's do_rebuild_from_text now wipes existing user tables
and metadata before reloading from text, so it works on both
fresh and populated databases. Source text is plumbed through
rebuild_from_text so the explicit rebuild logs to history.log
while the silent on-load rebuild from Iteration 3 stays silent.

Modal infrastructure (App.modal field + key routing + centered
overlay rendering + word-wrap) is reused by Iteration 4b's save
/ save as / load / new flows.

Tests: 314 passing (268 lib + 9 + 5 + 6 new + 9 + 17),
0 failing, 0 skipped. Clippy clean.

src/ui.rs

@@ -48,6 +48,117 @@ pub fn render(app: &mut App, theme: &Theme, frame: &mut Frame<'_>) {
     render_right_column(app, theme, frame, columns[1]);
     render_project_label(app, theme, frame, outer[1]);
     render_status_bar(app, theme, frame, outer[2]);
+
+    // Modal dialogs (rebuild confirm, save-as prompt, load
+    // picker, …) are drawn last so they overlay the rest of
+    // the frame.
+    if let Some(modal) = app.modal.as_ref() {
+        render_modal(modal, theme, frame, area);
+    }
+}
+
+fn render_modal(modal: &crate::app::Modal, theme: &Theme, frame: &mut Frame<'_>, area: Rect) {
+    use crate::app::Modal;
+    match modal {
+        Modal::RebuildConfirm(m) => render_rebuild_confirm(&m.summary, theme, frame, area),
+    }
+}
+
+/// Centred dialog with a one-paragraph body and a [Y]es/[N]o
+/// hint at the bottom. Sized at min(60 cols, area.width-4)
+/// wide and tall enough to fit the wrapped body plus 4 rows
+/// of chrome.
+fn render_rebuild_confirm(summary: &str, theme: &Theme, frame: &mut Frame<'_>, area: Rect) {
+    let dialog_w = area.width.min(60).saturating_sub(0);
+    let dialog_w = dialog_w.max(20);
+    let inner_w = dialog_w.saturating_sub(4) as usize;
+
+    let body_lines: Vec<String> = wrap_lines(summary, 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,
+    };
+
+    // Solid background panel so we cover whatever was beneath.
+    let bg = ratatui::widgets::Clear;
+    frame.render_widget(bg, dialog_area);
+
+    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(" Rebuild project ", 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("Continue?"));
+    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(" yes   "),
+        Span::styled(
+            "[N]",
+            Style::default()
+                .fg(theme.fg)
+                .add_modifier(Modifier::BOLD),
+        ),
+        Span::raw(" no   "),
+        Span::styled("Esc", Style::default().fg(theme.muted)),
+        Span::styled(" 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
+/// ASCII-friendly.
+fn wrap_lines(s: &str, width: usize) -> Vec<String> {
+    if width == 0 {
+        return vec![s.to_string()];
+    }
+    let mut lines: Vec<String> = Vec::new();
+    let mut current = String::new();
+    for word in s.split_whitespace() {
+        if !current.is_empty() && current.len() + 1 + word.len() <= width {
+            current.push(' ');
+        } else if !current.is_empty() {
+            lines.push(std::mem::take(&mut current));
+        }
+        current.push_str(word);
+    }
+    if !current.is_empty() {
+        lines.push(current);
+    }
+    if lines.is_empty() {
+        lines.push(String::new());
+    }
+    lines
 }
 
 fn render_project_label(app: &App, theme: &Theme, frame: &mut Frame<'_>, area: Rect) {
@@ -433,6 +544,20 @@ mod tests {
         insta::assert_snapshot!("one_shot_advanced_dark", snapshot);
     }
 
+    #[test]
+    fn rebuild_confirm_modal_snapshot() {
+        use crate::app::{Modal, RebuildConfirmModal};
+        let mut app = App::new();
+        app.modal = Some(Modal::RebuildConfirm(RebuildConfirmModal {
+            summary: "3 tables and 47 rows will be reconstructed; \
+                      the existing playground.db will be replaced"
+                .to_string(),
+        }));
+        let theme = Theme::dark();
+        let snapshot = render_to_string(&mut app, &theme, 80, 24);
+        insta::assert_snapshot!("rebuild_confirm_modal_dark", snapshot);
+    }
+
     #[test]
     fn populated_with_table_snapshot() {
         // Items panel lists tables; output panel shows the