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_client/lib/src/protocol/client.dart

@@ -835,14 +835,17 @@ class EndpointProfile extends _isc.EndpointRef {
         {},
       );
 
-  /// Removes your public profile, freeing its handle; nothing when you have
-  /// none. Throws [ProfileRefusedException] once your handle is fixed:
-  /// others refer to it.
-  _ida.Future<void> remove() => caller.callServerEndpoint<void>(
-    'halkyon_base.profile',
-    'remove',
-    {},
-  );
+  /// Removes what your public profile shows (display name, bio, links,
+  /// avatar), making it private again: the handle stays yours (Halkyon
+  /// Learn's ADR 0020, D27). Returns it; null when you have none. Throws
+  /// [ProfileRefusedException] once your handle is fixed: others refer to
+  /// it.
+  _ida.Future<_i8qdmv6n.Profile?> remove() =>
+      caller.callServerEndpoint<_i8qdmv6n.Profile?>(
+        'halkyon_base.profile',
+        'remove',
+        {},
+      );
 }
 
 /// The public profiles of others, found by their handles. Any signed-in