feat: set dogfooding demo workflow to on-demand trigger mode

Configure the example app to use trigger.mode: 'on-demand' so the pipeline
only runs when /glimpse is commented on a PR. Added issue_comment event
to the demo workflow to support this.

https://claude.ai/code/session_01F7qRXukhynYjUukzhaBzSK

Author: claude

.github/workflows/demo.yml

@@ -6,6 +6,8 @@ name: GitGlimpse Demo
 on:
   pull_request:
     types: [opened, synchronize]
+  issue_comment:
+    types: [created]
 
 jobs:
   demo:

examples/simple-app/git-glimpse.config.ts

@@ -9,6 +9,9 @@ const config: GitGlimpseConfig = {
     maxDuration: 20,
     viewport: { width: 960, height: 600 },
   },
+  trigger: {
+    mode: 'on-demand',
+  },
 };
 
 export default config;