Move portable README files into .github/ (declutter repo top page)

README-PORTABLE.txt and README-PORTABLE-ARM64.txt are release-packaging
inputs, not user-facing repo docs. Updated the two Copy-Item references
in release.yml and build-arm64-portable.yml; the file name inside the
distributed ZIP (README-PORTABLE.txt) is unchanged, so the portable
detection in FormMain.cs and the MSI leak checks are unaffected.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: seto77

README-PORTABLE-ARM64.txt .github/README-PORTABLE-ARM64.txtREADME-PORTABLE-ARM64.txt renamed to .github/README-PORTABLE-ARM64.txt

@@ -245,7 +245,9 @@ jobs:
           # portable 判定して Check Updates メニューを隠すため (codex レビュー指摘)
           Get-ChildItem $publishDir -Filter "*.pdb" | Remove-Item -Force
           Copy-Item "LICENSE.md" $publishDir -Force
-          Copy-Item "README-PORTABLE-ARM64.txt" (Join-Path $publishDir "README-PORTABLE.txt") -Force
+          # 260703Cl リポジトリトップページの整理のため README-PORTABLE*.txt を .github/ へ移動 (配布 ZIP 内の名前は不変)
+          # 旧: Copy-Item "README-PORTABLE-ARM64.txt" (Join-Path $publishDir "README-PORTABLE.txt") -Force
+          Copy-Item ".github/README-PORTABLE-ARM64.txt" (Join-Path $publishDir "README-PORTABLE.txt") -Force
 
           # 260611Cl 自前の ZIP 化はしない: Actions artifact はダウンロード時に GitHub が必ず ZIP で包むため、
           # ここで ZIP を作ると二重 ZIP (2 回解凍) になる (Surface 検証で指摘)。フォルダのまま artifact に渡し、

README-PORTABLE.txt .github/README-PORTABLE.txtREADME-PORTABLE.txt renamed to .github/README-PORTABLE.txt

@@ -296,7 +296,9 @@ jobs:
           foreach ($n in $natives) { Copy-Item $n.FullName $publishDir -Force; Write-Host "Bundled native: $($n.Name)" }
 
           Copy-Item "LICENSE.md" $publishDir -Force
-          Copy-Item "README-PORTABLE.txt" $publishDir -Force
+          # 260703Cl リポジトリトップページの整理のため README-PORTABLE*.txt を .github/ へ移動 (配布 ZIP 内の名前は不変)
+          # 旧: Copy-Item "README-PORTABLE.txt" $publishDir -Force
+          Copy-Item ".github/README-PORTABLE.txt" $publishDir -Force
 
           # 260602Cl 参照ライブラリの分離 pdb を配布物から除去 (ReciPro 本体は embedded のため元々 pdb なし)。
           Get-ChildItem $publishDir -Filter "*.pdb" | Remove-Item -Force