feat: add issue templates for Gitea (#22)

## Description

This PR implements issue templates for the lambda repository to improve issue tracking and developer experience.
The templates follow Gitea best practices and provide clear guidance for users when creating issues.
Three distinct templates were created to handle different types of issues: feature requests, bug reports, and general issues.

### Changes

- Created [.gitea/ISSUE_TEMPLATE/feature.md](.gitea/ISSUE_TEMPLATE/feature.md) for feature requests and enhancements.
- Created [.gitea/ISSUE_TEMPLATE/bug.md](.gitea/ISSUE_TEMPLATE/bug.md) for bug reports.
- Created [.gitea/ISSUE_TEMPLATE/general.md](.gitea/ISSUE_TEMPLATE/general.md) for general issues.
- Updated [CLAUDE.md](CLAUDE.md) with issue management and workflow documentation.

### Decisions

All templates use Markdown format with YAML frontmatter, following the existing PR template style.
Each template includes pre-populated metadata (title prefix, labels, target branch).
Templates provide inline HTML comments to guide users without cluttering the final issue.
The templates are consistent with conventional commit format (feat:, fix:, etc.).

## Benefits

Users will have clear guidance when creating issues, reducing back-and-forth communication.
Issues will be more structured and contain necessary information for developers.
Pre-populated labels and titles ensure consistent issue categorization.
The templates align with the existing PR template style for a cohesive experience.

## Checklist

- [x] Code follows conventional commit format.
- [x] Branch follows naming convention (`<type>/<description>`). Always use underscores.
- [x] Tests pass (if applicable).
- [x] Documentation updated (if applicable).

Reviewed-on: #22
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

.gitea/ISSUE_TEMPLATE/feature.md

@@ -0,0 +1,44 @@
+---
+name: "Feature Request"
+about: "Suggest a new feature or enhancement for the lambda interpreter."
+title: "feat: "
+ref: "main"
+assignees: []
+labels:
+  - enhancement
+---
+
+## Context
+
+<!--
+Describe the problem or limitation you're encountering.
+Explain why this feature would be valuable.
+-->
+
+## Proposed Solution
+
+<!--
+Describe your proposed solution or enhancement.
+Be specific about what you want to see implemented.
+-->
+
+## Alternatives Considered
+
+<!--
+List any alternative solutions or approaches you've considered.
+If none exist, omit this section.
+-->
+
+## Acceptance Criteria
+
+<!--
+List clear, testable criteria that define when this feature is complete.
+Use bullet points starting with •
+-->
+
+## Additional Context
+
+<!--
+Add any other context, screenshots, or examples about the feature request.
+If none exist, omit this section.
+-->