Enable GPU/WebGL and add persistent cache dirs

Enable hardware-accelerated rendering and persist GPU/cache data. Added a BrowserSettings() helper that enables WebGL and use it when creating Chrome/Content/MenuPopup browsers (src/app/nebula_controller.cpp). Configure CefSettings to use a persistent user data and cache directory (src/app/run.cpp) by calling nebula::ui::GetUserDataDirectory() and GetCacheDirectory(). Add command-line switches to initialize the GPU process and avoid sandbox/blocklist fallbacks (disable GPU sandbox, in-process-gpu, ignore-gpu-blocklist, enable-accelerated-video-decode, use ANGLE D3D11) to prevent GPU crashes and Chromium falling back to software rendering (src/cef/nebula_app.cpp). Implement GetUserDataDirectory() and GetCacheDirectory() (preferring %LOCALAPPDATA% with an executable-directory fallback) and expose them in the header (src/ui/paths.cpp, src/ui/paths.h). These changes ensure GPU shader caching, WebGL support, and smoother video/graphics behavior.

src/ui/paths.cpp

@@ -136,6 +136,44 @@ std::filesystem::path GetExecutableDirectory() {
     return std::filesystem::path(exe_path).parent_path();
 }
 
+std::filesystem::path GetUserDataDirectory() {
+    std::filesystem::path root;
+
+    wchar_t buffer[MAX_PATH] = {};
+    // Prefer %LOCALAPPDATA% so the profile follows Chromium conventions and
+    // survives executable relocation.
+    const DWORD length =
+        GetEnvironmentVariableW(L"LOCALAPPDATA", buffer, MAX_PATH);
+    if (length > 0 && length < MAX_PATH) {
+        root = std::filesystem::path(buffer);
+    } else {
+        // Fall back to a directory next to the executable so a portable
+        // install still gets a writable profile.
+        root = GetExecutableDirectory();
+    }
+
+    if (root.empty()) {
+        return {};
+    }
+
+    std::filesystem::path user_data = root / L"Nebula" / L"User Data";
+    std::error_code ec;
+    std::filesystem::create_directories(user_data, ec);
+    return user_data;
+}
+
+std::filesystem::path GetCacheDirectory() {
+    auto user_data = GetUserDataDirectory();
+    if (user_data.empty()) {
+        return {};
+    }
+
+    std::filesystem::path cache = user_data / L"Cache";
+    std::error_code ec;
+    std::filesystem::create_directories(cache, ec);
+    return cache;
+}
+
 std::filesystem::path GetUiPagePath(const std::wstring& page_name) {
     const auto exe_dir = GetExecutableDirectory();
     if (exe_dir.empty()) {