Prepare v0.4 release and open source docs

.github/pull_request_template.md

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+## Summary
+
+Describe what changed and why.
+
+## Screenshots Or Recordings
+
+Required for UI changes. Include before and after screenshots for changed UI, or at least one screenshot/recording for new UI.
+
+Each screenshot, recording, and committed media file included with this pull request must be under 1 MB.
+
+## Checks
+
+List the checks you ran:
+
+- [ ] `swift test`
+- [ ] `swift build -c release`
+- [ ] `scripts/verify-release-artifacts.sh`
+- [ ] Manual UI check
+- [ ] Not run, because:
+
+## Checklist
+
+- [ ] I read `CONTRIBUTING.md`.
+- [ ] This pull request is focused on one behavior, fix, or documentation change.
+- [ ] I updated `CHANGELOG.md` for user-visible changes, or this change is not user-visible.
+- [ ] UI changes include screenshots or recordings, or this pull request does not change UI.
+- [ ] Every screenshot, recording, and committed media file in this pull request is under 1 MB.
+- [ ] I explained any app-size impact from new assets, dependencies, or release packaging changes.