Create bug report issue template

Add a bug report template for GitHub issues.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,51 @@
+---
+name: Bug Report
+about: Something isn't working as expected
+title: "[Bug] "
+labels: bug
+assignees: ''
+---
+
+## Description
+
+A clear description of what the bug is.
+
+## Steps to Reproduce
+
+1. Go to '...'
+2. Click on '...'
+3. Scroll down to '...'
+4. See error
+
+## Expected Behavior
+
+What you expected to happen.
+
+## Actual Behavior
+
+What actually happened. Include error messages, console output, or screenshots if applicable.
+
+## Environment
+
+- **Browser:** (e.g. Firefox 128, Chrome 126, Safari 18)
+- **Device:** (e.g. Desktop, iPhone 15, Pixel 8)
+- **OS:** (e.g. Ubuntu 24.04, macOS 15, iOS 18)
+- **Docker version:** (run `docker --version`)
+- **Oikos version/commit:** (run `git rev-parse --short HEAD`)
+
+## Logs
+
+<details>
+<summary>Docker logs (if relevant)</summary>
+
+```
+docker compose logs oikos --tail=50
+```
+
+Paste output here.
+
+</details>
+
+## Additional Context
+
+Any other context — screenshots, related issues, or configuration details.