feat: add PR and issue templates for contributor guidance

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug Report
+about: Report a bug to help us improve
+title: '[Bug] '
+labels: bug
+---
+
+## Description
+<!-- A clear description of the bug -->
+
+## Steps to Reproduce
+1.
+2.
+3.
+
+## Expected Behavior
+<!-- What you expected to happen -->
+
+## Actual Behavior
+<!-- What actually happened -->
+
+## Environment
+- Sub2API Version:
+- Deployment Method: [Docker / Binary / Source]
+- OS:
+- Browser (if applicable):
+
+## Additional Context
+<!-- Screenshots, logs, or other relevant information -->

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature Request
+about: Suggest a new feature or improvement
+title: '[Feature] '
+labels: enhancement
+---
+
+## Problem
+<!-- What problem does this feature solve? -->
+
+## Proposed Solution
+<!-- How should this feature work? -->
+
+## Alternatives Considered
+<!-- Any alternative solutions you've considered -->
+
+## Additional Context
+<!-- Any other context, mockups, or examples -->

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+<!-- Brief description of the changes -->
+
+## Changes
+<!-- List key changes -->
+-
+
+## Type of Change
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Breaking change
+- [ ] Documentation update
+- [ ] Refactoring
+- [ ] CI/CD improvement
+
+## Testing
+- [ ] Unit tests pass (`make test-unit`)
+- [ ] Integration tests pass (`make test-integration`)
+- [ ] Frontend tests pass (`pnpm run test:run`)
+- [ ] Linting passes
+
+## Checklist
+- [ ] I have read the [DEV_GUIDE.md](DEV_GUIDE.md)
+- [ ] My code follows the project's coding conventions
+- [ ] I have added tests for my changes (if applicable)
+- [ ] I have updated documentation (if applicable)