Add live contact search to invitee input

The static datalist only carried the first 50 address book
contacts, so typed fragments could not match anything beyond
that. A new read-only GET /contacts/search endpoint queries
the full address book per keystroke, and a small vanilla JS
combobox shows the results and replaces only the fragment
after the last separator, so comma-separated lists keep
working. The server-rendered datalist remains as the no-JS
fallback; the JS removes the list attribute at runtime so
the native popup does not double the custom one.

tests/Unit/OCUtilStub.php

@@ -3,21 +3,57 @@
 declare(strict_types=1);
 
 /*
- * Minimal stand-in for the server class OC_Util, which is not part
- * of the OCP vendor package. Records addStyle() calls for assertions.
+ * Minimal stand-ins for server classes that are not part of
+ * the OCP vendor package. OC_Util records addStyle() calls,
+ * the OC classes satisfy the lookups that OCP\Util::addScript()
+ * triggers for app scripts.
  */
-if (!class_exists(\OC_Util::class, false)) {
-	class OC_Util
+namespace OC {
+	class AppScriptDependency
 	{
-		/** @var list<array{string, ?string, bool}> */
-		public static array $styles = [];
+		public function __construct(string $app, array $deps = []) {}
 
-		public static function addStyle(
-			string $application,
-			?string $file = null,
-			bool $prepend = false
-		): void {
-			self::$styles[] = [$application, $file, $prepend];
-		}
+		public function addDep(string $dep): void {}
 	}
 }
+
+namespace {
+	class OC
+	{
+		public static ?object $server = null;
+	}
+
+	class AToCalFakeL10NFactory
+	{
+		public function findLanguage(string $app): string
+		{
+			return 'en';
+		}
+	}
+
+	class AToCalFakeServer
+	{
+		public function get(string $serviceName): AToCalFakeL10NFactory
+		{
+			return new AToCalFakeL10NFactory();
+		}
+	}
+
+	if (!class_exists('OC_Util', false)) {
+		class OC_Util
+		{
+			/** @var list<array{string, ?string, bool}> */
+			public static array $styles = [];
+
+			public static function addStyle(
+				string $application,
+				?string $file = null,
+				bool $prepend = false
+			): void {
+				self::$styles[] = [$application, $file, $prepend];
+			}
+		}
+	}
+
+	OC::$server ??= new AToCalFakeServer();
+}