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>

CLAUDE.md

@@ -37,6 +37,31 @@ Use format: `<type>/<description>` with kebab-case.
 
 DO NOT advertise Claude.
 
+## Issue Management
+
+Use the `tea` CLI (Gitea command-line tool) for issue operations.
+
+**Common commands**:
+
+- `tea issues list` - List all issues.
+- `tea issues <number>` - View details of a specific issue.
+- `tea issues create --title "<title>" --body "<description>"` - Create a new issue.
+- `tea issues close <number>` - Close an issue.
+
+**Reading issues**: Use `tea issues <number>` to read the full details of an issue before starting work.
+
+## Issue Workflow
+
+When working on an issue:
+
+1. Read the issue using `tea issues <number>` to understand requirements.
+2. Create a feature branch following the branch naming convention.
+3. Make commits following the conventional commit format.
+4. Submit a pull request when ready.
+
+**Important**: Never commit directly to `main`.
+All work must be done in a feature branch and submitted via pull request.
+
 ## Pull Request Management
 
 Use the `tea` CLI (Gitea command-line tool) for PR operations instead of `gh`.