Add GitHub issue and PR templates

  - Add bug report and feature request issue templates
  - Add pull request template with Go-specific checklist
  - Improve community standards compliance

Author: willibrandon

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Report a bug in mtlog
+title: ''
+labels: bug
+assignees: ''
+---
+
+**Version**: (e.g., v0.2.0 or commit hash)
+
+**What happened?**
+A clear description of the bug.
+
+**Expected behavior**
+What you expected to happen.
+
+**Minimal reproduction**
+```go
+// Code that reproduces the issue
+```
+
+**Environment**
+- Go version: `go version`
+- OS: (e.g., linux/amd64)
+
+**Additional context**
+Any other relevant information.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest a new feature for mtlog
+title: ''
+labels: enhancement
+assignees: ''
+---
+
+**Is your feature request related to a problem?**
+A clear description of the problem.
+
+**Proposed solution**
+How you'd like to see it work.
+
+**Alternatives considered**
+Other approaches you've thought about.
+
+**Additional context**
+Any examples or use cases.

.github/pull_request_template.md

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+## Description
+Brief description of the changes.
+
+## Type of change
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Performance improvement
+- [ ] Documentation update
+
+## Checklist
+- [ ] Tests pass (`go test ./...`)
+- [ ] Linter passes (`golangci-lint run`)
+- [ ] Benchmarks checked (if performance-related)
+- [ ] Documentation updated (if needed)
+- [ ] Zero-allocation promise maintained (if applicable)
+
+## Additional notes
+Any other relevant information or context.