feat: add Windows PowerShell support and remote install one-liners

- remote-install.sh: POSIX one-liner (curl | sh), downloads archive to tmpdir
- remote-install.ps1: Windows one-liner (irm | iex), fully native PowerShell
- install.ps1: Native Windows installer calling all .ps1 post-install scripts
- bin/mosaic-link-runtime-assets.ps1: Syncs runtime config files
- bin/mosaic-sync-skills.ps1: Clones skills, links via directory junctions
- bin/mosaic-migrate-local-skills.ps1: Migrates local skills to junctions
- bin/mosaic-doctor.ps1: Health audit for Windows environments

Directory junctions used instead of symlinks (no elevation required).
All junction operations fall back to file copy on failure.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

remote-install.ps1

@@ -0,0 +1,37 @@
+# Mosaic Bootstrap — Remote Installer (Windows PowerShell)
+#
+# One-liner:
+#   irm https://git.mosaicstack.dev/mosaic/bootstrap/raw/branch/main/remote-install.ps1 | iex
+#
+# Or explicit:
+#   powershell -ExecutionPolicy Bypass -File remote-install.ps1
+#
+$ErrorActionPreference = "Stop"
+
+$ArchiveUrl = "https://git.mosaicstack.dev/mosaic/bootstrap/archive/main.zip"
+$WorkDir = Join-Path $env:TEMP "mosaic-bootstrap-$PID"
+$ZipPath = "$WorkDir.zip"
+
+try {
+    Write-Host "[mosaic] Downloading bootstrap archive..."
+    New-Item -ItemType Directory -Path $WorkDir -Force | Out-Null
+    Invoke-WebRequest -Uri $ArchiveUrl -OutFile $ZipPath -UseBasicParsing
+
+    Write-Host "[mosaic] Extracting..."
+    Expand-Archive -Path $ZipPath -DestinationPath $WorkDir -Force
+
+    $InstallScript = Join-Path $WorkDir "bootstrap\install.ps1"
+    if (-not (Test-Path $InstallScript)) {
+        throw "install.ps1 not found in archive"
+    }
+
+    Write-Host "[mosaic] Running install..."
+    & $InstallScript
+
+    Write-Host "[mosaic] Done."
+}
+finally {
+    Write-Host "[mosaic] Cleaning up temporary files..."
+    Remove-Item -Path $ZipPath -Force -ErrorAction SilentlyContinue
+    Remove-Item -Path $WorkDir -Recurse -Force -ErrorAction SilentlyContinue
+}