Add dbis_core issue templates and code owners

.gitea/CODEOWNERS

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+* @d-bis/Owners

.gitea/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Report a problem in dbis_core
+title: "[bug]: "
+labels: bug
+---
+
+## What happened
+
+## Expected behavior
+
+## Steps to reproduce
+
+## Environment
+
+- branch:
+- browser:
+- device:
+- screenshot/log:

.gitea/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an improvement for dbis_core
+title: "[feature]: "
+labels: enhancement
+---
+
+## Request
+
+## Motivation
+
+## Suggested implementation
+
+## Acceptance criteria

.gitea/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+- 
+
+## Validation
+
+- [ ] `pnpm lint`
+- [ ] `pnpm typecheck`
+- [ ] Gitea workflow checked
+
+## Notes
+
+-