feat: add pull request template (#5)

## Description

Added a standardized pull request template to improve PR quality and consistency. The template provides a clear structure for contributors to follow when creating PRs.

The template includes:
- Title placeholder following conventional commit format (`<type>: <description>`)
- Description section with guidance on context, rationale, and changes
- Optional Decisions section for architectural choices
- Benefits section to highlight improvements
- Checklist for conventional commits, branch naming, tests, and documentation

### Decisions

Created the template in `.gitea/PULL_REQUEST_TEMPLATE/default.md` to support multiple template types in the future.

## Benefits

- Ensures PRs follow project conventions (conventional commits, branch naming)
- Provides clear structure for describing changes
- Helps reviewers understand context and benefits
- Reduces back-and-forth by reminding contributors of requirements
- Supports future expansion with additional template types

Reviewed-on: #5
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

.gitea/PULL_REQUEST_TEMPLATE/default.md

@@ -0,0 +1,32 @@
+---
+title: "<type>: <description>"
+---
+
+## Description
+
+<!--
+First, describe the context for the PR.
+Then, explain why the PR exists.
+Finally, in concise, sentence-long bullets, explain each change.
+-->
+
+### Decisions
+
+<!--
+List any major architectural decisions here.
+If none exist, omit this section.
+-->
+
+## Benefits
+
+<!--
+List any major benefits here.
+How would this PR improve the codebase/product?
+-->
+
+## Checklist
+
+- [ ] Code follows conventional commit format.
+- [ ] Branch follows naming convention (`<type>/<description>`).
+- [ ] Tests pass (if applicable).
+- [ ] Documentation updated (if applicable).