Migrate data paths to ~/.local/share/fluorine/, add native build, fix %command% and system Proton scanning

- All data paths migrated from ~/.var/app/com.fluorine.manager/ to
  ~/.local/share/fluorine/ so native and Flatpak builds share the same
  instances, plugins, and configs
- New fluorinepaths.h/.cpp with fluorineDataDir() helper and one-time
  migration from old path (writes MOVED.txt breadcrumb)
- New libs/nak/src/paths.rs as Rust equivalent (data_dir())
- Strip %command% tokens from launch wrapper in protonlauncher.cpp
- Always scan /usr/share/steam/compatibilitytools.d/ for system Proton
  packages (Arch installs Proton there); add Flatpak filesystem permission
- Native build (build-native.sh) installs to ~/.local/share/fluorine/
  with desktop entry and ~/.local/bin symlink instead of portable zip
- build-flatpak.sh wrapper for Flatpak builds
- Fix container locale (LANG=C.UTF-8) for AutoUic warnings
- Fix prefixExists() to handle both compatdata and pfx directory layouts
- Fix globalInstancesRootPath() to use fluorineDataDir() on Linux
- Fix umu-run Flatpak lookup to use fluorineDataDir()
- Update README with build instructions and Arch dependency list

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

1 files changed, 18 insertions, 9 deletions

diff --git a/libs/installer_fomod/src/fomodinstallerdialog.cpp b/libs/installer_fomod/src/fomodinstallerdialog.cpp
index 0fa6bfc..f675e3d 100644
--- a/libs/installer_fomod/src/fomodinstallerdialog.cpp
+++ b/libs/installer_fomod/src/fomodinstallerdialog.cpp
@@ -127,11 +127,15 @@ int FomodInstallerDialog::bomOffset(const QByteArray& buffer)
   static const unsigned char BOM_UTF8[]    = {0xEF, 0xBB, 0xBF};
   static const unsigned char BOM_UTF16BE[] = {0xFE, 0xFF};
   static const unsigned char BOM_UTF16LE[] = {0xFF, 0xFE};
+  auto startsWithBytes = [&buffer](const unsigned char* bytes, qsizetype size) {
+    return buffer.startsWith(
+        QByteArrayView(reinterpret_cast<const char*>(bytes), size));
+  };
 
-  if (buffer.startsWith(reinterpret_cast<const char*>(BOM_UTF8)))
+  if (startsWithBytes(BOM_UTF8, sizeof(BOM_UTF8)))
     return 3;
-  if (buffer.startsWith(reinterpret_cast<const char*>(BOM_UTF16BE)) ||
-      buffer.startsWith(reinterpret_cast<const char*>(BOM_UTF16LE)))
+  if (startsWithBytes(BOM_UTF16BE, sizeof(BOM_UTF16BE)) ||
+      startsWithBytes(BOM_UTF16LE, sizeof(BOM_UTF16LE)))
     return 2;
 
   return 0;
@@ -150,25 +154,30 @@ QByteArray skipXmlHeader(QIODevice& file)
   static const unsigned char UTF16LE[]     = {0x3C, 0x00, 0x3F, 0x00};
   static const unsigned char UTF16BE[]     = {0x00, 0x3C, 0x00, 0x3F};
   static const unsigned char UTF8[]        = {0x3C, 0x3F, 0x78, 0x6D};
+  auto startsWithBytes = [](const QByteArray& bytes, const unsigned char* prefix,
+                            qsizetype size) {
+    return bytes.startsWith(
+        QByteArrayView(reinterpret_cast<const char*>(prefix), size));
+  };
 
   file.seek(0);
   QByteArray rawBytes = file.read(4);
   QTextStream stream(&file);
   int bom = 0;
-  if (rawBytes.startsWith((const char*)UTF16LE_BOM)) {
+  if (startsWithBytes(rawBytes, UTF16LE_BOM, sizeof(UTF16LE_BOM))) {
     stream.setEncoding(QStringConverter::Encoding::Utf16LE);
     bom = 2;
-  } else if (rawBytes.startsWith((const char*)UTF16BE_BOM)) {
+  } else if (startsWithBytes(rawBytes, UTF16BE_BOM, sizeof(UTF16BE_BOM))) {
     stream.setEncoding(QStringConverter::Encoding::Utf16BE);
     bom = 2;
-  } else if (rawBytes.startsWith((const char*)UTF8_BOM)) {
+  } else if (startsWithBytes(rawBytes, UTF8_BOM, sizeof(UTF8_BOM))) {
     stream.setEncoding(QStringConverter::Encoding::Utf8);
     bom = 3;
-  } else if (rawBytes.startsWith(QByteArray((const char*)UTF16LE, 4))) {
+  } else if (startsWithBytes(rawBytes, UTF16LE, sizeof(UTF16LE))) {
     stream.setEncoding(QStringConverter::Encoding::Utf16LE);
-  } else if (rawBytes.startsWith(QByteArray((const char*)UTF16BE, 4))) {
+  } else if (startsWithBytes(rawBytes, UTF16BE, sizeof(UTF16BE))) {
     stream.setEncoding(QStringConverter::Encoding::Utf16BE);
-  } else if (rawBytes.startsWith(QByteArray((const char*)UTF8, 4))) {
+  } else if (startsWithBytes(rawBytes, UTF8, sizeof(UTF8))) {
     stream.setEncoding(QStringConverter::Encoding::Utf8);
   }  // otherwise maybe the textstream knows the encoding?