Add subsystem discovery to product and levelup init commands

[kanfil]

Summary

This PR adds subsystem detection capabilities to the product and levelup extensions, mirroring the functionality already present in the architect extension.

Changes

Product Extension:

• Renamed "Feature Area Detection" → "Subsystem Detection" for consistency
• Updated all terminology from "feature area" to "subsystem"
• Added detect_subsystems function to bash/powershell scripts
• Added --json and --no-decompose flag support

LevelUp Extension:

• Added new Phase 0: Sub-System Detection (~90 lines of documentation)
• Added detect_subsystems function to bash/powershell scripts
• Added --no-decompose flag support
• Updated outline to include new phase

Technical Details

The subsystem detection logic:

• Analyzes directory structure (src/, services/, modules/, apps/)
• Detects docker-compose services
• Checks for Node.js workspaces (monorepo)
• Detects Python namespace packages
• Checks for Go modules under cmd/

Files Modified

• extensions/product/commands/init.md - Terminology update
• extensions/product/scripts/bash/setup-product.sh - Add detection function
• extensions/product/scripts/powershell/setup-product.ps1 - Add detection function
• extensions/levelup/commands/init.md - Add Phase 0
• extensions/levelup/scripts/bash/setup-levelup.sh - Add detection function
• extensions/levelup/scripts/powershell/setup-levelup.ps1 - Add detection function