docs: update all markdown documentation

- README.md: Update tech stack versions, simplify content, add links to docs
- CONTRIBUTING.md: Add commit guidelines, testing instructions, PR process
- SECURITY.md: Add security measures, vulnerability reporting process
- PULL_REQUEST_TEMPLATE.md: Add conventional commit types, breaking change section
- Remove outdated plan documents (already implemented or superseded)
- architecture.md: Already updated with comprehensive system documentation
- release-engineering.md: Already updated with current pipeline status

.github/PULL_REQUEST_TEMPLATE.md

@@ -4,22 +4,37 @@
 
 ## Type of Change
 
-- [ ] Bug fix (non-breaking change that fixes an issue)
-- [ ] New feature (non-breaking change that adds functionality)
-- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
-- [ ] Documentation update
+- [ ] `feat` - New feature (minor version bump)
+- [ ] `fix` - Bug fix (patch version bump)
+- [ ] `perf` - Performance improvement (patch version bump)
+- [ ] `docs` - Documentation only
+- [ ] `refactor` - Code refactoring
+- [ ] `test` - Adding/updating tests
+- [ ] `ci` - CI/CD changes
+- [ ] `chore` - Maintenance tasks
+
+## Breaking Changes
+
+- [ ] This is a breaking change (major version bump)
+
+**If breaking, describe the migration path:**
 
 ## Checklist
 
-- [ ] I have followed the [Contributing Guidelines](CONTRIBUTING.md)
+- [ ] Commit messages follow [Conventional Commits](CONTRIBUTING.md#commit-guidelines)
 - [ ] Lint passes (`npm run lint`)
 - [ ] Build succeeds (`npm run build`)
-- [ ] I have tested my changes locally
+- [ ] Tests pass (`npm run test:run`)
+- [ ] API documentation updated (if applicable)
+
+## Testing
+
+<!-- Describe how you tested these changes -->
 
 ## Screenshots (if applicable)
 
-<!-- Add screenshots here -->
+<!-- Add screenshots for UI changes -->
 
 ## Related Issues
 
-<!-- Link any related issues: Closes #123 -->
+<!-- Link issues: Closes #123, Fixes #456 -->