refactor: standardize install patterns across Makefiles

[HarryCampion]

• Update Makefile.presentation: Add install-marp target with global check and local install fallback to ${INSTALL_DIR}/node_modules/.bin/marp
• Update Makefile.agentic: Add COPILOT_BIN variable with global check, update install-copilot to check global first, then local ${INSTALL_DIR}
• Add comprehensive test suite (test_install_patterns.py) with 25 tests:
  • Mock tests for install behavior without side effects
  • Integration tests using make dry-run for CI pipelines
  • Pattern consistency tests across all Makefiles
• Exception: gh CLI only checks global (no straightforward local install)

[HarryCampion]

Standardize Install Patterns Across Makefiles

Summary

This PR standardizes the installation patterns across all Makefiles to follow a consistent approach:

1. Check if globally installed (command -v <tool>)
2. Check if locally installed in ${INSTALL_DIR} (defaults to ./bin)
3. Install to local directory if neither exists

This ensures tools are installed in the project's ./bin directory rather than globally, providing better isolation and reproducibility across environments.

Changes

Makefile.presentation

• Added new install-marp target following the standard pattern
• Added MARP_BIN variable: checks global first → falls back to ${INSTALL_DIR}/node_modules/.bin/marp
• Changed from npm install -g (global) to npm install --prefix "${INSTALL_DIR}" (local)
• All presentation targets now depend on install-marp

Makefile.agentic

• Added COPILOT_BIN variable: checks global first → falls back to ${INSTALL_DIR}/copilot
• Updated install-copilot to check global installation before checking local
• Updated all targets to use ${COPILOT_BIN} instead of hardcoded ${INSTALL_DIR}/copilot

Exceptions

• gh CLI (Makefile.gh): Only checks for global installation and displays a warning if not found - there's no straightforward way to install it locally to ./bin

Tests Added

New test file tests/test_rhiza/test_install_patterns.py with 25 tests:

Test Class	Description
TestInstallPatternConsistency	Validates all install targets exist and follow the global-check-then-local pattern
TestMockInstallBehavior	Mock-based tests for install behavior without side effects
TestIntegrationInstallPatterns	Dry-run integration tests that work in CI pipelines
TestInstallDirVariable	Tests for INSTALL_DIR variable behavior
TestInstallTargetDocumentation	Validates all install targets have help comments

Install Pattern Reference

Tool	Makefile	Pattern
uv/uvx	Makefile	✅ Global check → ${INSTALL_DIR} fallback
gh	Makefile.gh	⚠️ Global check only (exception)
copilot	Makefile.agentic	✅ Global check → ${INSTALL_DIR} fallback
marp	Makefile.presentation	✅ Global check → ${INSTALL_DIR} fallback

Testing

# Run all install pattern tests
make test

# Or run just the install pattern tests
pytest tests/test_rhiza/test_install_patterns.py -v

All 94 tests pass (1 skipped).