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>

docs/adr/0020-sign-in-with-simplelogin.md

@@ -103,7 +103,10 @@
   one `HandleField` with its `HandleCheckCubit` (asked 300 ms after typing pauses, only
   for the handle typed last, the instance's suggestion free without asking) serves the
   password setup's handle step, between the phrase check and the code, and
-  SimpleLogin's sign-up and keys steps.
+  SimpleLogin's sign-up and keys steps. Then D27: `profile.remove` (and the register's
+  `removeProfile`, members asking it) empties the display name, bio, links and their
+  checks and the avatar, keeps the row with its handle, and returns what is left; Learn's
+  profile form starts afresh from it and offers no removing while nothing is filled in.
 - **Builds on:** ADR 0010 (email sign-in), ADR 0011 (profile pages), ADR 0016 (the
   register), ADR 0017 (a password, TOTP and the keys).
 - **Changes:** ADR 0017's way in on an instance that offers SimpleLogin (its keys, their