feat(command-palette): add fuzzy model/provider filtering, expose ModelPaletteEntry, and show active model with provider in UI header

- Introduce `ModelPaletteEntry` and re‑export it for external use.
- Extend `CommandPalette` with dynamic sources (models, providers) and methods to refresh suggestions based on `:model` and `:provider` prefixes.
- Implement fuzzy matching via `match_score` and subsequence checks for richer suggestion ranking.
- Add `provider` command spec and completions.
- Update UI to display “Model (Provider)” in the header and use the new active model label helper.
- Wire catalog updates throughout `ChatApp` (model palette entries, command palette refresh on state changes, model picker integration).

crates/owlen-tui/src/ui.rs

@@ -504,12 +504,9 @@ fn render_header(frame: &mut Frame<'_>, area: Rect, app: &ChatApp) {
             .fg(theme.focused_panel_border)
             .add_modifier(Modifier::BOLD),
     );
-    let provider_span = Span::styled(
-        app.current_provider().to_string(),
-        Style::default().fg(theme.text),
-    );
-    let model_span = Span::styled(
-        app.selected_model().to_string(),
+    let model_label = app.active_model_label();
+    let model_with_provider_span = Span::styled(
+        format!("{} ({})", model_label, app.current_provider()),
         Style::default()
             .fg(theme.user_message_role)
             .add_modifier(Modifier::BOLD),
@@ -527,11 +524,8 @@ fn render_header(frame: &mut Frame<'_>, area: Rect, app: &ChatApp) {
         Line::default(),
         Line::from(vec![
             Span::raw(" "),
-            Span::styled("Provider: ", Style::default().fg(theme.placeholder)),
-            provider_span,
-            Span::raw("  "),
-            Span::styled("Model: ", Style::default().fg(theme.placeholder)),
-            model_span,
+            Span::styled("Model (Provider): ", Style::default().fg(theme.placeholder)),
+            model_with_provider_span,
         ]),
     ];