docs: add pull request template

PULL_REQUEST_TEMPLATE.md

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+## Student Submission
+
+**Name:** 
+**Role:** [Backend/Frontend/Database/Graphics]
+**Lesson:** [1/2/3]
+
+## Changes Made
+
+### Role-Specific Checklist:
+
+#### Backend Developer (Dima)
+- [ ] Prize structure implemented (15 levels)
+- [ ] Game session management
+- [ ] Answer validation logic
+- [ ] Lifeline functionality (50:50, Phone Friend)
+- [ ] All routes working
+
+#### Frontend Developer (Inna)  
+- [ ] Question display working
+- [ ] Answer selection handling
+- [ ] Prize ladder updates
+- [ ] Lifeline buttons functional
+- [ ] Game flow complete
+
+#### Database Designer (Danil)
+- [ ] 150 Russian culture questions
+- [ ] Increasing difficulty progression  
+- [ ] Plausible wrong answers
+- [ ] Categories: history, geography, culture, entertainment
+
+#### Graphics Artist (Artyom)
+- [ ] Russian color theme applied
+- [ ] Enhanced styling from basic template
+- [ ] Visual improvements
+- [ ] Visual assets including logo
+- [ ] Audio assets including sound effects
+- [ ] Consistent design
+
+## Testing Performed
+- [ ] My component works independently
+- [ ] No errors in console
+- [ ] Responsive design checked
+
+## Questions/Blockers