Add auto-bootstrap in `apm install` when no apm.yml exists

[danielmeppiel]

Summary

Enable apm install <package> to automatically create a minimal apm.yml when none exists, matching npm's behavior where npm install <package> works in any directory.

Current Behavior

$ apm install danielmeppiel/design-guidelines
Error: No apm.yml found. Run 'apm init' first.

Target Behavior

$ apm install danielmeppiel/design-guidelines
✨ Created apm.yml
✓ Added danielmeppiel/design-guidelines to apm.yml
✓ Installed danielmeppiel/design-guidelines

# apm.yml is now created with minimal config + the installed package

Implementation Requirements

Logic Flow

def install(ctx, packages, ...):
    apm_yml_exists = Path('apm.yml').exists()
    
    # NEW: Auto-bootstrap when packages specified but no apm.yml
    if not apm_yml_exists and packages:
        _create_minimal_apm_yml()  # Reuse from issue #13
        _rich_success("Created apm.yml", symbol="sparkles")
    
    # Error only when NO apm.yml AND NO packages
    if not apm_yml_exists and not packages:
        _rich_error("No apm.yml found")
        _rich_info("💡 Run 'apm init' to create one, or:")
        _rich_info("   apm install <org/repo> to auto-create + install")
        sys.exit(1)
    
    # Continue with existing install logic...

Integration with Issue #13

• Reuse the minimal apm.yml generator from apm init refactor
• Same auto-detection logic for project metadata
• Consistent output format

Scenarios

Scenario 1: No apm.yml, WITH packages

cd existing-repo
apm install myorg/standards myorg/chatmodes
# ✨ Creates minimal apm.yml
# ✓ Adds both packages to dependencies
# ✓ Installs both packages

Scenario 2: No apm.yml, NO packages

cd existing-repo
apm install
# ❌ Error with helpful message pointing to:
#    - apm init (create empty manifest)
#    - apm install <package> (create + install)

Scenario 3: Has apm.yml (existing behavior preserved)

cd project-with-apm-yml
apm install                  # Install existing deps
apm install myorg/new-pkg    # Add to apm.yml + install

Acceptance Criteria

• apm install org/pkg in directory without apm.yml creates minimal manifest
• Auto-created apm.yml includes the specified package in dependencies
• Success message clearly indicates apm.yml was created
• apm install without packages and without apm.yml shows helpful error
• Error message suggests both apm init and apm install <package> options
• Existing behavior preserved when apm.yml already exists
• Tests cover all scenarios (with/without manifest, with/without packages)
• Integration with minimal init generator from issue Refactor apm init to minimal-only mode (breaking change) #13

Dependencies

• Requires issue Refactor apm init to minimal-only mode (breaking change) #13 (minimal init refactor) to be completed first
• Shares auto-detection and minimal apm.yml generation logic

Related

Part of npm-parity redesign for brownfield adoption