docs: Improve PR template with checklist and testing strategy (#6148)

* docs: Improve PR template with checklist and testing strategy

Add structured checklist and testing strategy section to the PR
template to improve developer experience and AI readiness scoring.

Changes:
- Add Checks section with test, sign-off, and conventional commits items
- Add Testing Strategy section (unit tests, manual tests, not required)
- Retain existing sections (description, issue link, misc)

Signed-off-by: Ambient Code Bot <bot@ambient-code.local>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Ambient Code Bot <bot@ambient-code.local>

* docs: Add integration tests to PR template checklist

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Ambient Code Bot <bot@ambient-code.local>

---------

Signed-off-by: Ambient Code Bot <bot@ambient-code.local>
Co-authored-by: Ambient Code Bot <bot@ambient-code.local>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

.github/pull_request_template.md

@@ -11,7 +11,7 @@
 
 # What this PR does / why we need it:
 <!--
-Outline what you're doing
+Outline what you're doing and why.
 -->
 
 # Which issue(s) this PR fixes:
@@ -20,6 +20,16 @@ Outline what you're doing
 Usage: `Fixes #<issue number>`, or `Fixes (paste link of issue)`.
 -->
 
+# Checks
+- [ ] I've made sure the tests are passing.
+- [ ] My commits are signed off (`git commit -s`)
+- [ ] My PR title follows [conventional commits](https://www.conventionalcommits.org/) format
+
+## Testing Strategy
+- [ ] Unit tests
+- [ ] Integration tests
+- [ ] Manual tests
+- [ ] Testing is not required for this change
 
 # Misc
 <!--