docs(adr): ADR 0021 accepted, the assistant's boundaries (D7–D30)

The developer's decisions of 25 Oct, reviewing ADR 0021 whole:

- What an assistant may see and do (D7–D12): the scope of each question
  (the parts ticked, the studyset, its tree, the library), looked up
  through read-only tools the app answers on the device; private
  studysets out of a wider scope unless switched on, and a warning
  whenever one's content would go to a remote model, Lumo included, as
  no provider keeps a question confidential while its model answers;
  changes only as drafts; progress never; text first, an image when
  ticked or asked for.
- What it keeps, does and where it lives (D13–D18): conversations kept
  sealed with the person's own key; four features (questions about what
  is open, cards from text, explaining a miss, checking a written
  answer); grants and limits in halkyon_base, the adapters in a package
  of their own (halkyon_llm, BSD-3-Clause); the proposal's points 4–8
  and 10 as written; the warning once per studyset and assistant; built
  for v0.21.0.
- Sign-ups and operators (D19–D26): SIGN_UP open, approval or closed;
  the first operator by SQL, others named in the app; suspending an
  approved account; a wait screen with a matching code the operator
  checks with the person; 14 days, 10 waiting.
- What people are told and what never goes (D27–D30): the app and a
  privacy page of each instance's own; others' posts only with their
  author's switch, a copy's licence being its agreement; an opaque ID
  per person for the provider.

ADR 0022 and Learn's AGENTS.md now point to it as accepted.

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/0022-no-hand-off-and-no-connector.md

@@ -5,8 +5,8 @@
 - **Supersedes:** ADR 0006 (Claude reads studysets through a connector on the instance),
   and the hand-off to an AI assistant outside the app (decided 10 and 14 Oct 2026, Learn's
   `AGENTS.md`).
-- **Followed by:** ADR 0021 (an assistant on the instance, on its operator's keys), still
-  proposed.
+- **Followed by:** ADR 0021 (an assistant on the instance, on its operator's keys),
+  accepted 25 Oct 2026.
 
 ## Context