refactor(ui): improve rendering, feedback, and help system

Improve UI rendering and feedback:

- `src/draw.rs` :
    - Automatically enter Help mode if the model is empty.
    - Render the `HelpWidget` with the current help page.
    - Render the `WhichKeyWidget` when a transient keymap is active.
- `src/ui/tile_bar.rs` : Use more descriptive labels for axes (e.g., "Row",
  "Col", "Pag").
- `src/ui/view_panel.rs` :
    - Include an axis summary (e.g., "R:Region C:Product") next to view
      names.
    - Refactor `ViewContent` to hold a reference to the `Model` .
- `src/ui/effect.rs` : Add error feedback to `AddItem` , `AddItemInGroup` ,
  and `AddFormula` when operations fail.
- `src/ui/help.rs` : Refactor `HelpWidget` into a multi-page system.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/gemma-4-26B-A4B-it-GGUF:UD-Q5_K_XL)

src/draw.rs

@@ -26,6 +26,7 @@ use crate::ui::import_wizard_ui::ImportWizardWidget;
 use crate::ui::panel::Panel;
 use crate::ui::tile_bar::TileBar;
 use crate::ui::view_panel::ViewContent;
+use crate::ui::which_key::WhichKeyWidget;
 
 struct TuiContext<'a> {
     terminal: Terminal<CrosstermBackend<&'a mut Stdout>>,
@@ -60,6 +61,8 @@ pub fn run_tui(
 
     if let Some(json) = import_value {
         app.start_import_wizard(json);
+    } else if app.is_empty_model() {
+        app.mode = AppMode::Help;
     }
 
     loop {
@@ -162,7 +165,7 @@ fn draw(f: &mut Frame, app: &App) {
 
     // Overlays (rendered last so they appear on top)
     if matches!(app.mode, AppMode::Help) {
-        f.render_widget(HelpWidget, size);
+        f.render_widget(HelpWidget::new(app.help_page), size);
     }
     if matches!(app.mode, AppMode::ImportWizard) {
         if let Some(wizard) = &app.wizard {
@@ -173,6 +176,12 @@ fn draw(f: &mut Frame, app: &App) {
     if app.is_empty_model() && matches!(app.mode, AppMode::Normal | AppMode::CommandMode { .. }) {
         draw_welcome(f, main_chunks[1]);
     }
+
+    // Which-key popup: show available completions after a prefix key
+    if let Some(ref km) = app.transient_keymap {
+        let hints = km.binding_hints();
+        f.render_widget(WhichKeyWidget::new(&hints), size);
+    }
 }
 
 fn draw_title(f: &mut Frame, area: Rect, app: &App) {