chore: add open-source governance files (GPLv3 + contributing docs)

Add standard open-source project files:
- LICENSE.md — GNU GPL v3.0 or later (verbatim)
- CONTRIBUTING.md — setup, workflow, and required AI-usage disclosure
- CONTRIBUTORS.md — maintainers, contributors, AI-assistance policy
- CODE_OF_CONDUCT.md — Contributor Covenant 2.1
- SECURITY.md — private vulnerability reporting
- .gitea/ISSUE_TEMPLATE/* + PULL_REQUEST_TEMPLATE.md
- README: License section (Copyright (C) 2026 Runic Gateway)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XmHdsbnLzDMAVQkAoTQSBe

.gitea/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,41 @@
+---
+name: Bug report
+about: Report something that is broken or behaving unexpectedly
+title: "[bug] "
+labels:
+  - bug
+---
+
+## Summary
+
+<!-- A clear, concise description of the bug. -->
+
+## Steps to reproduce
+
+1.
+2.
+3.
+
+## Expected behavior
+
+<!-- What you expected to happen. -->
+
+## Actual behavior
+
+<!-- What actually happened. Include exact error messages and logs if you have them. -->
+
+## Environment
+
+- Component / repo:
+- Version or commit:
+- OS / runtime (Node, Rust, ServUO, browser…):
+- Deployment (Docker Compose, local dev, bare metal…):
+
+## Additional context
+
+<!-- Screenshots, config (with secrets redacted), anything else that helps. -->
+
+<!--
+  Security issue? Do NOT file it here. See SECURITY.md and email
+  whitlocktech@gmail.com instead.
+-->