Replace hardcoded font with check for default fonts, fall back to

inter/roboto
Settings: use font detection function
GeneralTab: let user know that it uses default fonts and falls back to
inter/roboto
FontService: add proper checks for default fonts (sans & mono)

Commons/Settings.qml

@@ -203,6 +203,17 @@ Singleton {
     BluetoothService.init()
   }
 
+  // -----------------------------------------------------
+  // Update font defaults when system fonts are detected
+  function updateFontDefaults() {
+    if (FontService.systemFontsDetected) {
+      Logger.log("Settings", "Updating font defaults with detected system fonts")
+      adapter.ui.fontDefault = FontService.getSystemSansFont()
+      adapter.ui.fontFixed = FontService.getSystemMonospaceFont()
+      adapter.ui.fontBillboard = FontService.getSystemDisplayFont()
+    }
+  }
+
   // -----------------------------------------------------
   // Ensure directories exist before FileView tries to read files
   Component.onCompleted: {
@@ -213,6 +224,9 @@ Singleton {
 
     // Mark directories as created and trigger file loading
     directoriesCreated = true
+
+    // Connect to font service signal to update defaults when system fonts are detected
+    FontService.systemFontsDetected.connect(updateFontDefaults)
   }
 
   // Don't write settings to disk immediately
@@ -415,9 +429,9 @@ Singleton {
 
       // ui
       property JsonObject ui: JsonObject {
-        property string fontDefault: "Roboto"
-        property string fontFixed: "DejaVu Sans Mono"
-        property string fontBillboard: "Inter"
+        property string fontDefault: FontService.getSystemSansFont()
+        property string fontFixed: FontService.getSystemMonospaceFont()
+        property string fontBillboard: FontService.getSystemDisplayFont()
         property list<var> monitorsScaling: []
         property bool idleInhibitorEnabled: false
       }