feat: UxUrl — native URL / phone / email detection + tap launcher

Sync FFI from Dart into platform detectors:
- iOS / macOS: NSDataDetector(.link | .phoneNumber) + a tight bare-domain
  pass that requires `/` or `?` (so `etc.` / `v1.2.3` don't false-positive
  while `example.com/path` does match). NFKD-fold the phone capture so
  full-width / Arabic-Indic digits collapse to ASCII; stop the digit run
  at the first letter so `+1 555 1234 ext.99` doesn't fuse the extension.
- Android: JNI into android.util.Patterns (WEB_URL / EMAIL_ADDRESS / PHONE)
  via a cached JavaVM, std::call_once for init, full per-call
  ExceptionCheck coverage. UTF-16→UTF-8 conversion is hand-rolled to dodge
  the Modified-UTF-8 / CESU-8 incompatibility with Dart's utf8.decode.

`UxUrl.launch(url)` is the matching tap action. Channel side dispatches via
UIApplication / NSWorkspace / Intent.ACTION_VIEW. Dart-side gates the URL
against a scheme allowlist (http, https, mailto, tel, sms, banlu, tg),
rejects bidi-override controls (U+202A..E / U+2066..9) to prevent visual
spoofs, and blocks USSD / MMI tel: codes containing `*` or `#`.

Library/native cleanup along the way:
- Renamed libux_keyboard.so to libux.so (also covers sensor + url).
- Collapsed three near-identical FFI loader stanzas across keyboard / sensor
  / url into a shared lib/src/_ffi.dart with `uxLib` + typed `uxLookupX`
  helpers.

lib/src/_ffi.dart

@@ -0,0 +1,58 @@
+import 'dart:ffi';
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+
+DynamicLibrary? _open() {
+  if (kIsWeb) return null;
+  try {
+    if (Platform.isIOS || Platform.isMacOS) return DynamicLibrary.process();
+    if (Platform.isAndroid) return DynamicLibrary.open('libux.so');
+  } catch (_) {
+    return null;
+  }
+  return null;
+}
+
+/// `null` on web, unsupported platforms, or load failure.
+final DynamicLibrary? uxLib = _open();
+
+double Function()? uxLookupDouble(String name) {
+  final lib = uxLib;
+  if (lib == null) return null;
+  try {
+    return lib.lookup<NativeFunction<Double Function()>>(name).asFunction();
+  } catch (_) {
+    return null;
+  }
+}
+
+int Function()? uxLookupInt32(String name) {
+  final lib = uxLib;
+  if (lib == null) return null;
+  try {
+    return lib.lookup<NativeFunction<Int32 Function()>>(name).asFunction();
+  } catch (_) {
+    return null;
+  }
+}
+
+void Function()? uxLookupVoid(String name) {
+  final lib = uxLib;
+  if (lib == null) return null;
+  try {
+    return lib.lookup<NativeFunction<Void Function()>>(name).asFunction();
+  } catch (_) {
+    return null;
+  }
+}
+
+void Function(double)? uxLookupVoidDouble(String name) {
+  final lib = uxLib;
+  if (lib == null) return null;
+  try {
+    return lib.lookup<NativeFunction<Void Function(Double)>>(name).asFunction();
+  } catch (_) {
+    return null;
+  }
+}