feat: Refactor service management scripts to use a unified dev script

- Added package.json to manage development scripts.
- Updated restart-services.ps1 to call the new dev script for starting services.
- Refactored start-admin.ps1, start-backend.ps1, start-frontend.ps1, and start-mcp.ps1 to utilize the dev script for starting respective services.
- Enhanced stop-services.ps1 to improve process termination logic by matching command patterns.

start-backend.ps1

@@ -5,23 +5,7 @@ param(
 $ErrorActionPreference = "Stop"
 
 $repoRoot = Split-Path -Parent $MyInvocation.MyCommand.Path
-$backendDir = Join-Path $repoRoot "backend"
+$devScript = Join-Path $repoRoot "dev.ps1"
 
-if (-not (Test-Path $backendDir)) {
-  throw "Backend directory not found: $backendDir"
-}
-
-Push-Location $backendDir
-
-try {
-  $env:DATABASE_URL = $DatabaseUrl
-  Write-Host "[backend] DATABASE_URL set to $DatabaseUrl" -ForegroundColor Cyan
-  Write-Host "[backend] Starting Loco.rs server..." -ForegroundColor Green
-  cargo loco start 2>&1
-  if ($LASTEXITCODE -ne 0) {
-    throw "cargo loco start failed"
-  }
-}
-finally {
-  Pop-Location
-}
+& $devScript -Only backend -DatabaseUrl $DatabaseUrl
+exit $LASTEXITCODE