Enable model upgrade popup even when selected model is no longer in picker (#8802)

With `config.toml`:
```
model = "gpt-5.1-codex"
```
(where `gpt-5.1-codex` has `show_in_picker: false` in
[`model_presets.rs`](https://github.com/openai/codex/blob/main/codex-rs/core/src/models_manager/model_presets.rs);
this happens if the user hasn't used codex in a while so they didn't see
the popup before their model was changed to `show_in_picker: false`)

The upgrade picker used to not show (because `gpt-5.1-codex` was
filtered out of the model list in code). Now, the filtering is done
downstream in tui and app-server, so the model upgrade popup shows:

<img width="1503" height="227" alt="Screenshot 2026-01-06 at 5 04 37 PM"
src="https://github.com/user-attachments/assets/26144cc2-0b3f-4674-ac17-e476781ec548"
/>

codex-rs/tui2/src/chatwidget.rs

@@ -2106,7 +2106,7 @@ impl ChatWidget {
         let models = self.models_manager.try_list_models(&self.config).ok()?;
         models
             .iter()
-            .find(|preset| preset.model == NUDGE_MODEL_SLUG)
+            .find(|preset| preset.show_in_picker && preset.model == NUDGE_MODEL_SLUG)
             .cloned()
     }
 
@@ -2222,6 +2222,14 @@ impl ChatWidget {
                     return;
                 }
             };
+        self.open_model_popup_with_presets(presets);
+    }
+
+    pub(crate) fn open_model_popup_with_presets(&mut self, presets: Vec<ModelPreset>) {
+        let presets: Vec<ModelPreset> = presets
+            .into_iter()
+            .filter(|preset| preset.show_in_picker)
+            .collect();
 
         let current_label = presets
             .iter()