fix: prevent .SRCINFO creation in project root

- Use subshell for cd in aur-update-all recipe
- Add .SRCINFO to root .gitignore

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

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

.gitignore

@@ -11,3 +11,4 @@ aur/*/*.tar.gz
 aur/*/*.tar.xz
 aur/*/*.pkg.tar.*
 # Keep PKGBUILD and .SRCINFO tracked
+.SRCINFO