chore: add GitHub issue templates for bug reports and feature requests

Adopts issue template pattern from opencode-antigravity-auth:
- Bug report template with [BUG] prefix and 6-item checklist
- Feature request template with [FEATURE] prefix
- Config disables blank issues, adds links to Google Cloud Support, TOS, and Discussions

Co-Authored-By: Claude <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,42 @@
+---
+name: Bug Report
+about: Report a bug or issue with the proxy
+title: '[BUG] '
+labels: bug
+assignees: ''
+---
+
+**Bug Description**
+A clear and concise description of the bug.
+
+**Steps to Reproduce**
+1.
+2.
+3.
+
+**Expected Behavior**
+What should happen.
+
+**Actual Behavior**
+What actually happens.
+
+**Environment**
+- Claude Code version:
+- antigravity-claude-proxy version:
+- Operating System:
+- Node.js version:
+
+**Logs (if applicable)**
+
+
+**Checklist**
+Please confirm:
+- [ ] I've updated antigravity-claude-proxy to the latest version
+- [ ] The bug exists in the latest version
+- [ ] I'm using this proxy for personal development only
+- [ ] I have an active Google Cloud project with Antigravity enabled
+- [ ] This issue is not related to attempting commercial use or TOS violations
+- [ ] I've reviewed the README troubleshooting section
+
+**Additional Context**
+Add any other relevant information.