Installer build: pre-flight diagnostics + verbose ISCC output

ISCC's default error message ("The system cannot find the path
specified.") doesn't say which file failed, which made the Gitea
runner failure undebugable. Two changes:

1. Before invoking ISCC, log a one-line summary per source path the
   .iss references: file count, longest path length, root. Also dump
   HKLM\...\FileSystem\LongPathsEnabled so MAX_PATH issues are
   immediately obvious.
2. Pass /Qp to ISCC so it prints each file as it processes; the line
   right before the error tells us which source file ISCC choked on.

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

scripts/build-installer.ps1

@@ -53,14 +53,46 @@ if ($LASTEXITCODE -ne 0) { throw 'service publish failed' }
     -c $Configuration -r win-x64 --self-contained false -o $publishGui | Out-Host
 if ($LASTEXITCODE -ne 0) { throw 'GUI publish failed' }
 
-# 2. Compile installer.
+# 2. Pre-flight: confirm every source path the .iss references exists, and
+#    surface the longest path so MAX_PATH issues are obvious in the log.
+function Show-SourcePath($label, $path, [switch]$Recursive) {
+    if (-not (Test-Path $path)) { Write-Warning "MISSING $label : $path"; return }
+    $items = if ($Recursive) {
+        Get-ChildItem $path -Recurse -File -ErrorAction SilentlyContinue
+    } else {
+        Get-ChildItem $path -File -ErrorAction SilentlyContinue
+    }
+    $count   = ($items | Measure-Object).Count
+    $longest = ($items | Measure-Object -Maximum -Property { $_.FullName.Length }).Maximum
+    Write-Host ("  {0,-30} files={1,-5} longestPath={2,-5} root={3}" -f $label, $count, $longest, $path)
+}
+
+Write-Host ""
+Write-Host "--- pre-flight: source paths the .iss will read ---" -ForegroundColor Cyan
+Show-SourcePath 'publish\service'        $publishSvc                              -Recursive
+Show-SourcePath 'publish\gui'            $publishGui                              -Recursive
+Show-SourcePath 'scripts'                (Join-Path $repoRoot 'scripts')
+Show-SourcePath 'scripts\examples'       (Join-Path $repoRoot 'scripts\examples') -Recursive
+Show-SourcePath 'docs'                   (Join-Path $repoRoot 'docs')             -Recursive
+Show-SourcePath 'resources'              (Join-Path $repoRoot 'resources')
+Show-SourcePath 'README.md (file)'       (Join-Path $repoRoot 'README.md')
+
+$lpe = (Get-ItemProperty 'HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem' `
+            -Name LongPathsEnabled -ErrorAction SilentlyContinue).LongPathsEnabled
+Write-Host "  LongPathsEnabled (HKLM): $lpe"
+Write-Host ""
+
+# 3. Compile installer.
 $iscc = Find-InnoCompiler
 $iss = Join-Path $repoRoot 'installer\webhook-server.iss'
 $dist = Join-Path $repoRoot 'dist'
 New-Item -ItemType Directory -Path $dist -Force | Out-Null
 
 Write-Host "Compiling installer with $iscc"
-& $iscc "/DAppVersion=$version" $iss
+# /Qp gives quiet output but still prints the line each source file matches,
+# which surfaces the exact source path that ISCC fails on (the default mode
+# only logs "The system cannot find the path specified." with no detail).
+& $iscc "/DAppVersion=$version" "/Qp" $iss
 if ($LASTEXITCODE -ne 0) { throw 'Inno Setup compile failed' }
 
 $out = Get-Item (Join-Path $dist "WebhookServer-Setup-$version.exe")