feat(base)!: removing a profile makes it private (ADR 0020, D27)

Every account keeps a handle now, so removing a public profile no
longer deletes it and frees the handle: it takes away what the profile
shows and leaves it private, as a profile is until its person goes
public (D5).

- `profile.remove` and the register's `removeProfile` (members ask the
  register) empty the display name, bio, links with their checks and
  the avatar, keep the row with its handle, and return what is left,
  null for none. `/@handle` and `profiles.byHandle` then answer as for
  a handle nobody has. Once the person has published, removing is
  refused as before.
- Learn: the profile form starts afresh from what is left, "Remove
  profile" shows only while something is filled in, and the dialog says
  the handle stays.
- The module's README and ADR 0020 amended.

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_base_server/test/integration/test_tools/serverpod_test_tools.dart

@@ -1720,7 +1720,9 @@ class _ProfileEndpoint {
     });
   }
 
-  _ida.Future<void> remove(_ist.TestSessionBuilder sessionBuilder) async {
+  _ida.Future<_it4tom37.Profile?> remove(
+    _ist.TestSessionBuilder sessionBuilder,
+  ) async {
     return _ist.callAwaitableFunctionAndHandleExceptions(() async {
       var _localUniqueSession =
           (sessionBuilder as _ist.InternalTestSessionBuilder).internalBuild(
@@ -1740,7 +1742,7 @@ class _ProfileEndpoint {
                   _localUniqueSession,
                   _localCallContext.arguments,
                 )
-                as _ida.Future<void>);
+                as _ida.Future<_it4tom37.Profile?>);
         return _localReturnValue;
       } finally {
         await _localUniqueSession.close();