feat: add Drone CI pipelines, Jest unit tests, and Prettier check

Add Drone CI with server build/test and format check pipelines.
Add unit tests for password utils and recurrenceExpander.
Add check_format script, fix Jest config to ignore dist/,
remove dead CaldavService.test.ts, apply Prettier formatting.

apps/client/src/app/(tabs)/settings.tsx

@@ -45,7 +45,9 @@ const CaldavTextInput = ({
   const { theme } = useThemeStore();
   return (
     <View className="flex flex-row items-center py-1">
-      <Text className="ml-4 w-24" style={{ color: theme.textPrimary }}>{title}:</Text>
+      <Text className="ml-4 w-24" style={{ color: theme.textPrimary }}>
+        {title}:
+      </Text>
       <CustomTextInput
         className="flex-1 mr-4 px-3 py-2"
         text={value}
@@ -111,7 +113,13 @@ const CaldavSettings = () => {
   );
 
   const saveConfig = async () => {
-    showFeedback(setSaveFeedback, saveTimer, "Speichere Konfiguration...", false, true);
+    showFeedback(
+      setSaveFeedback,
+      saveTimer,
+      "Speichere Konfiguration...",
+      false,
+      true,
+    );
     try {
       const saved = await CaldavConfigService.saveConfig(
         serverUrl,
@@ -119,9 +127,19 @@ const CaldavSettings = () => {
         password,
       );
       setConfig(saved);
-      showFeedback(setSaveFeedback, saveTimer, "Konfiguration wurde gespeichert", false);
+      showFeedback(
+        setSaveFeedback,
+        saveTimer,
+        "Konfiguration wurde gespeichert",
+        false,
+      );
     } catch {
-      showFeedback(setSaveFeedback, saveTimer, "Fehler beim Speichern der Konfiguration", true);
+      showFeedback(
+        setSaveFeedback,
+        saveTimer,
+        "Fehler beim Speichern der Konfiguration",
+        true,
+      );
     }
   };
 
@@ -129,9 +147,19 @@ const CaldavSettings = () => {
     showFeedback(setSyncFeedback, syncTimer, "Synchronisiere...", false, true);
     try {
       await CaldavConfigService.sync();
-      showFeedback(setSyncFeedback, syncTimer, "Synchronisierung erfolgreich", false);
+      showFeedback(
+        setSyncFeedback,
+        syncTimer,
+        "Synchronisierung erfolgreich",
+        false,
+      );
     } catch {
-      showFeedback(setSyncFeedback, syncTimer, "Fehler beim Synchronisieren", true);
+      showFeedback(
+        setSyncFeedback,
+        syncTimer,
+        "Fehler beim Synchronisieren",
+        true,
+      );
     }
   };