chore: add GitHub automation and fix rand vulnerability

GitHub Actions:
- Add Dependabot for weekly dependency updates (cargo, github-actions)
- Add PR labeler workflow with file-based auto-labeling
- Add issue/PR templates (bug report, feature request, PR template)
- Fix release.yml artifact paths and labeler.yml config syntax
Security:
- Upgrade rand 0.8 → 0.10 to fix RUSTSEC-2026-0097 unsoundness
- Update screenshot.rs for rand 0.10 API (thread_rng → rng, gen_range → random_range)

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,23 @@
+# Pull Request Template
+
+## Description
+Please include a summary of the change and which issue is fixed (if relevant).
+
+## Type of Change
+- [ ] Bug fix (non-breaking change that fixes an issue)
+- [ ] New feature (non-breaking change that adds functionality)
+- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
+- [ ] Documentation update
+- [ ] Refactoring
+
+## How Has This Been Tested?
+Please describe the tests that you ran to verify your changes.
+
+## Checklist
+- [ ] My code follows the style guidelines of this project
+- [ ] I have performed a self-review of my own code
+- [ ] I have commented my code, particularly in hard-to-understand areas
+- [ ] I have made corresponding changes to the documentation
+- [ ] My changes generate no new warnings
+- [ ] I have added tests that prove my fix is effective or that my feature works
+- [ ] New and existing unit tests pass locally with my changes