feat(effect): add changes_mode method to Effect trait and use it in ExecuteCommand

Add a `changes_mode` method to the `Effect` trait with a default implementation
returning `false` . Implement this method for the `ChangeMode` effect to return
`true` . Update the command execution logic to use `e.changes_mode()` instead of
string matching on formatted output. Adjust the corresponding test to assert the
presence of a mode‑changing effect directly via the new method, removing the
temporary debug string.

This change introduces a clear, typed way to detect mode‑changing effects,
improving readability and reducing reliance on string inspection.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (bartowski/nvidia_Nemotron-Cascade-2-30B-A3B-GGUF)

src/ui/effect.rs

@@ -10,6 +10,10 @@ use super::app::{App, AppMode};
 /// Effects know how to apply themselves to the App.
 pub trait Effect: Debug {
     fn apply(&self, app: &mut App);
+    /// Whether this effect changes the app mode.
+    fn changes_mode(&self) -> bool {
+        false
+    }
 }
 
 // ── Model mutations ──────────────────────────────────────────────────────────
@@ -328,6 +332,9 @@ impl Effect for ChangeMode {
     fn apply(&self, app: &mut App) {
         app.mode = self.0.clone();
     }
+    fn changes_mode(&self) -> bool {
+        true
+    }
 }
 
 #[derive(Debug)]