chore: add open-source community files and CI workflow

- LICENSE (MIT)
- SECURITY.md (vulnerability reporting policy)
- CONTRIBUTING.md (development setup and contribution guide)
- CI workflow (fmt, clippy, test on push/PR)
- Issue templates (bug report, feature request)
- Dependabot config (cargo + github-actions weekly)
- Cargo.toml workspace metadata (license, repository, description)

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: cargo
+    directory: "/"
+    schedule:
+      interval: weekly
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: weekly