Add community contribution templates

.github/pull_request_template.md

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+## Summary
+
+- 
+
+## What Changed
+
+- 
+
+## Visual QA
+
+Please attach screenshots for visual changes.
+
+- [ ] Checked at least one dense text slide
+- [ ] Checked at least one image slide
+- [ ] Checked navigation / ESC overview / low-power mode when relevant
+
+## Validation
+
+- [ ] `node scripts/validate-swiss-deck.mjs path/to/index.html`
+- [ ] Manual browser review
+
+## Notes
+
+Any tradeoffs, limitations, or follow-up work: