docs: add contributor, security, and forge templates

Add CONTRIBUTING/SECURITY/CHANGELOG, Gitea issue and PR templates, and README guidance for Gitea metadata and releases.

Made-with: Cursor

.gitea/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,30 @@
+---
+name: Bug report
+about: Report incorrect results, crashes, or broken workflows
+title: "[bug] "
+labels: bug
+---
+
+## Summary
+
+<!-- What went wrong? -->
+
+## Expected behavior
+
+## Actual behavior
+
+## Reproduction
+
+<!-- Minimal steps, XML snippet or path under data/cases/, API request JSON, etc. -->
+
+## Environment
+
+- OS:
+- Node (`node -v`):
+- Commit / tag:
+
+## Logs / output
+
+```
+(paste relevant logs)
+```