Add markdown linting and pre-push build validation to git hooks

[thomasnemer]

Summary

This PR implements the improvements requested in issue #115 by adding:

• Markdown linting to the pre-commit hook
• Pre-push build validation to prevent broken code from reaching the remote

Changes Made

1. Markdown Linting Integration

Added rumdl as markdown linter:

• Added rumdl (Rust Markdown Linter) to .mise.toml tools
• Created mise run markdown-check task for checking markdown files
• Created mise run markdown-fix task for auto-fixing markdown issues

Updated pre-commit hook:

• Added markdown linting step to hk.pkl pre-commit hook
• Automatically checks all **/*.md files
• Auto-fixes violations when possible (blank lines, heading spacing, list formatting)
• Re-stages fixed markdown files automatically

2. Pre-Push Build Validation

Added pre-push hook:

• New pre-push hook in hk.pkl that runs mise run build-ci
• Ensures library, tests, and examples build successfully before push
• Verifies no formatting violations exist
• Prevents CI failures and broken pushes

3. Markdown Formatting Applied

• Fixed 343 auto-fixable markdown issues across 32 files
• Addressed spacing, blank lines, and list formatting issues
• Remaining line length warnings (MD013) left for manual review

Testing

• ✅ Git hooks installed successfully with hk install
• ✅ Pre-commit hook runs clang-format on C++ files
• ✅ Pre-commit hook runs rumdl fmt on markdown files
• ✅ Pre-push hook runs full build validation
• ✅ Committed and pushed successfully with new hooks

Benefits

1. Consistency: All markdown files follow consistent formatting style
2. Early detection: Catch build failures locally before pushing
3. CI efficiency: Fewer failed CI runs due to formatting or build issues
4. Documentation quality: Better docs with enforced markdown standards

Related Issue

Closes #115

Documentation

• Git hooks configuration documented in hk.pkl with inline comments
• Mise tasks documented with clear descriptions
• Hook behavior documented in CONTRIBUTING.md

Fixes #115