chore: remove redundant build artifacts and test outputs from git

### Changes:
1. **Removed from git tracking**:
   - client/12.2StoryToVideo/StoryToVideoGenerator.dmg (67MB) - Installation package should not be tracked
   - server/gin-server/static/tasks/*/result.mp4 - Generated test output
   - server/gin-server/static/tasks/124/*.png - Generated test images

2. **Updated .gitignore**:
   - Added *.dmg, *.pkg, *.exe exclusions
   - Added client/*/.xcode/ and client/*/Release/ directories
   - Added server/gin-server/static/tasks/*/ pattern to ignore all generated test outputs
   - Excluded all client build distribution artifacts

### Rationale:
- Binary installers and test outputs should be generated, not committed
- Reduces repository size and avoids unnecessary CI/CD artifacts
- Local builds remain unaffected due to .gitignore rules

Author: 胡傲东

.gitignore

@@ -69,13 +69,23 @@ debug/
 # Client specific
 client/build/
 client/dist-app/
+client/*/.xcode/
+client/*/Release/
 client/*/StoryToVideoGenerator.app/
+client/*/*.dmg
 storytovideo.app/
 storytovideo*.zip
+*.dmg
+*.pkg
+*.exe
 
 # Server logs
 server/log/
 
+# Server test outputs (generated media)
+server/gin-server/static/tasks/*/
+server/static/tasks/*/
+
 # Word documents (not source code)
 *.docx
 *.pdf