Add delete confirmation dialog for kanban cards

When clicking the trash icon to delete a feature card, users now see a
confirmation dialog asking them to confirm the deletion. This prevents
accidental deletions and provides a clear cancel option.

- Added Dialog component with confirm/cancel buttons to kanban-card
- Updated mock electron API to support test feature injection via __mockFeatures
- Added test utilities for delete confirmation dialog interactions
- Fixed test infrastructure to properly load mock features

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/src/lib/electron.ts

@@ -150,6 +150,11 @@ export const getElectronAPI = (): ElectronAPI => {
       }
       // Return mock data based on file type
       if (filePath.endsWith("feature_list.json")) {
+        // Check if test has set mock features via global variable
+        const testFeatures = (window as any).__mockFeatures;
+        if (testFeatures !== undefined) {
+          return { success: true, content: JSON.stringify(testFeatures, null, 2) };
+        }
         return { success: true, content: JSON.stringify(mockFeatures, null, 2) };
       }
       if (filePath.endsWith("categories.json")) {
@@ -290,6 +295,10 @@ export const getElectronAPI = (): ElectronAPI => {
       if (mockFileSystem[filePath] !== undefined) {
         return true;
       }
+      // Check if test has set mock features via global variable
+      if (filePath.endsWith("feature_list.json") && (window as any).__mockFeatures !== undefined) {
+        return true;
+      }
       // Legacy mock files for backwards compatibility
       if (filePath.endsWith("feature_list.json") && !filePath.includes(".automaker")) {
         return true;