feat(cli): add upgrade system foundation (Sprint 1)

[iammukeshm]

Summary

This PR adds the foundation for the FSH CLI upgrade system, enabling projects to track their versions and eventually upgrade to newer FSH releases.

Sprint 1 Deliverables

• ✅ Manifest generation - .fsh/manifest.json created during fsh new
• ✅ FshManifest model - Tracks project config, versions, and customizations
• ✅ fsh version command - Shows CLI and project version info
• ✅ fsh upgrade command - Skeleton with --check and --apply flags

New Files

File	Purpose
Models/FshManifest.cs	Manifest model with JSON serialization
Commands/VersionCommand.cs	Display version information
Commands/UpgradeCommand.cs	Upgrade command skeleton

Manifest Structure

{
  "fshVersion": "10.0.0",
  "createdAt": "2026-01-27T02:50:00Z",
  "cliVersion": "10.0.0",
  "options": {
    "type": "api-blazor",
    "architecture": "monolith",
    "database": "postgres",
    "modules": ["identity", "multitenancy", "auditing"]
  },
  "tracking": {
    "buildingBlocks": {
      "Core": "10.0.0",
      "Web": "10.0.0",
      "Persistence": "10.0.0",
      "Infrastructure": "10.0.0"
    },
    "customizations": []
  }
}

Next Steps

• Sprint 2: GitHub API integration for release fetching, version comparison
• Sprint 3: Package updater, interactive diff viewer
• Sprint 4: Polish + fsh add module command

Testing

# Create a new project (generates manifest)
fsh new TestApp --preset quickstart

# Check version info
fsh version --path ./TestApp

# See upgrade command help
fsh upgrade