feat(cli): add install-module command for custom module installation

[AlexSuprun]

Summary

• Adds new CLI command install-module for installing custom BMAD modules from local paths
• Allows users to skip the full interactive installer when adding custom modules

Usage

npx bmad-method install-module /path/to/module [--force]

What it does

• Validates module path and module.yaml
• Finds existing BMAD installation
• Uses ModuleManager to install module files
• Regenerates manifests and IDE commands (Claude Code)
• Updates manifest with new module

Test plan

• Tested with spark-workshop custom module
• Verified module files copied to _bmad/
• Verified manifest updated
• Verified Claude Code commands generated

Closes #962

[bmadcode]

Instead of a new CLI, I was thinking of just extending the existing with some shortcuts / command line options. also there is another PR in progress that I think does this. Main idea being with the exisitng cli for example pass in the path to the module at command init and it would just do the addition of initial install of that module/agent/workflow.