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/dependabot.yml

@@ -0,0 +1,32 @@
+# Dependabot configuration for RustLock
+
+version: 2
+
+updates:
+  - package-ecosystem: "cargo"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "09:00"
+      timezone: "UTC"
+    open-pull-requests-limit: 10
+    labels:
+      - "dependencies"
+      - "rust"
+    commit-message:
+      prefix: "deps"
+    reviewers:
+      - "JorySeverijnse"
+    versioning-strategy: "increase"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "09:00"
+      timezone: "UTC"
+    labels:
+      - "dependencies"
+      - "github-actions"