fix(app)!: instances over plain HTTP are refused, but on this machine

What the app sends an instance (the proofs that sign in, the keys'
wrappings, every request a session carries) must not be read or changed on
the way, so an instance is reached over HTTPS, or over plain HTTP only on
this machine (localhost, 127.0.0.0/8, ::1), as Jellyfin servers are. An
address over plain HTTP elsewhere is refused before anything is sent there.
One kept from before is never opened: the app says why, and offers another
instance or removing it from the device, never dropping it silently.
Development builds still use their own instance over HTTP (an emulator
reaches the developer's machine as 10.0.2.2); releases never.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_app/lib/l10n/halkyon_app_localizations_en.dart

@@ -32,6 +32,22 @@ class HalkyonAppLocalizationsEn extends HalkyonAppLocalizations {
   @override
   String get instanceAddressInvalid => 'This isn\'t an address.';
 
+  @override
+  String instanceAddressInsecure(String app) {
+    return '$app reaches instances over HTTPS only, so that nobody on the way reads or changes what it sends. Ask for the instance\'s HTTPS address.';
+  }
+
+  @override
+  String instanceInsecure(String name, String app) {
+    return '$name is reached over plain HTTP, where anyone on the way could read and change what $app sends, so $app no longer opens it. Its account stays on $name and on this device. Use another instance, or remove it from this device.';
+  }
+
+  @override
+  String get instanceInsecureUseAnother => 'Use another instance';
+
+  @override
+  String get instanceInsecureRemove => 'Remove from this device';
+
   @override
   String get instanceAddressRequired => 'Enter the address of an instance.';