Add scripts/install.ps1 — PowerShell port of install.sh

Native cmdlet equivalent of install.sh: same behavior (copy each
skills/<name>/ into ~\.claude\skills\<name>\, skip if SKILL.md is
missing, support $env:CLAUDE_SKILLS_DIR override and -Names filter).

Removes bash dependency on Windows — no need to invoke git-bash from
pwsh, mirrors the existing build.sh / build.ps1 pair.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/install.ps1

@@ -0,0 +1,46 @@
+# Install skills/<name>/ into ~\.claude\skills\<name>\ (or $env:CLAUDE_SKILLS_DIR)
+# Usage: install.ps1 [-Names <name1>,<name2>]   (no args = all)
+#
+# PowerShell port of install.sh — same behavior, native cmdlets, no bash dependency.
+
+[CmdletBinding()]
+param(
+    [string[]]$Names = @()
+)
+
+$ErrorActionPreference = 'Stop'
+
+$root = Split-Path -Parent $PSScriptRoot
+$src  = Join-Path $root 'skills'
+
+if ($env:CLAUDE_SKILLS_DIR) {
+    $target = $env:CLAUDE_SKILLS_DIR
+} else {
+    $target = Join-Path $env:USERPROFILE '.claude\skills'
+}
+
+if (-not (Test-Path $target)) {
+    New-Item -ItemType Directory -Force -Path $target | Out-Null
+}
+
+if ($Names.Count -eq 0) {
+    $Names = Get-ChildItem -Path $src -Directory | Sort-Object Name | Select-Object -ExpandProperty Name
+}
+
+foreach ($name in $Names) {
+    $srcDir = Join-Path $src $name
+    $dstDir = Join-Path $target $name
+    if (-not (Test-Path $srcDir -PathType Container)) {
+        Write-Warning "skip: $name (not found in skills/)"
+        continue
+    }
+    if (-not (Test-Path (Join-Path $srcDir 'SKILL.md'))) {
+        Write-Warning "skip: $name (missing SKILL.md)"
+        continue
+    }
+    if (Test-Path $dstDir) {
+        Remove-Item -Recurse -Force $dstDir
+    }
+    Copy-Item -Recurse $srcDir $dstDir
+    Write-Host "installed: $name -> $dstDir"
+}