chore: add contribution workflow and experiment templates

.gitea/ISSUE_TEMPLATE/bug.md

@@ -0,0 +1,31 @@
+---
+name: Bug report
+about: Report a reproducible problem in an existing experiment
+title: ""
+---
+
+## Experiment and version
+
+Link the affected directory and identify the commit or version.
+
+## What happened?
+
+Describe the observed result and what you expected.
+
+## Reproduce it
+
+1.
+2.
+3.
+
+## Environment
+
+Operating system, browser or runtime version, and relevant configuration. Use placeholder values for private configuration.
+
+## Evidence
+
+Include a minimal example or redacted screenshot/log. Do not post credentials, tokens, personal records, or private URLs.
+
+## Checks already tried
+
+State what you tried and what happened.