feat: improve dashboard and connection workflows

- add connection delete endpoint and update connection list handling

- expand dashboard visualization behavior

- update helpers/header and project TODO tracking

app/lib/helpers.php

@@ -297,8 +297,83 @@ HTML, [
  * Sonstiges
  * ========================= */
 
-// TODO: Weitere Helfer nach Bedarf
-// - Datum formatieren
-// - Bytes → MB
-// - UUID erzeugen
-// - SVG-Koordinaten normalisieren
+/**
+ * Formatiert Datum/Uhrzeit robust oder gibt Fallback zurueck.
+ *
+ * @param string|null $value
+ * @param string $format
+ * @param string $fallback
+ * @return string
+ */
+function formatDateTime(?string $value, string $format = 'd.m.Y H:i', string $fallback = '-'): string
+{
+    if ($value === null || trim($value) === '') {
+        return $fallback;
+    }
+
+    $timestamp = strtotime($value);
+    if ($timestamp === false) {
+        return $fallback;
+    }
+
+    return date($format, $timestamp);
+}
+
+/**
+ * Formatiert Byte-Werte in menschenlesbare Einheit.
+ *
+ * @param int|float $bytes
+ * @param int $precision
+ * @return string
+ */
+function formatBytes($bytes, int $precision = 2): string
+{
+    $value = (float)$bytes;
+    if ($value <= 0) {
+        return '0 B';
+    }
+
+    $units = ['B', 'KB', 'MB', 'GB', 'TB'];
+    $power = min((int)floor(log($value, 1024)), count($units) - 1);
+    $scaled = $value / (1024 ** $power);
+
+    return number_format($scaled, $precision, '.', '') . ' ' . $units[$power];
+}
+
+/**
+ * Erzeugt eine UUID v4.
+ *
+ * @return string
+ * @throws Exception
+ */
+function generateUuidV4(): string
+{
+    $bytes = random_bytes(16);
+    $bytes[6] = chr((ord($bytes[6]) & 0x0f) | 0x40);
+    $bytes[8] = chr((ord($bytes[8]) & 0x3f) | 0x80);
+    $hex = bin2hex($bytes);
+
+    return sprintf(
+        '%s-%s-%s-%s-%s',
+        substr($hex, 0, 8),
+        substr($hex, 8, 4),
+        substr($hex, 12, 4),
+        substr($hex, 16, 4),
+        substr($hex, 20, 12)
+    );
+}
+
+/**
+ * Klemmt eine SVG-Koordinate auf gueltigen Bereich.
+ *
+ * @param float $value
+ * @param float $min
+ * @param float $max
+ * @param int $precision
+ * @return float
+ */
+function normalizeSvgCoordinate(float $value, float $min, float $max, int $precision = 2): float
+{
+    $normalized = max($min, min($max, $value));
+    return round($normalized, $precision);
+}