feat: add issue templates for Gitea

Added three issue templates to improve issue tracking:
- Feature request template for new features and enhancements.
- Bug report template for reporting bugs and unexpected behavior.
- General issue template for issues that don't fit other categories.

Templates follow Gitea best practices with proper frontmatter metadata.
Each template includes clear sections with inline comments to guide users.

Updated CLAUDE.md with issue management and workflow documentation.

Closes #21

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.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.
+-->