feat(learn): a private studyset goes to an assistant only once agreed

ADR 0021, D9 and D17. Before a question sends a private studyset's
content to a remote model, through the parts chosen or a wider reach
with private studysets switched on, a warning names the studysets, the
provider's host and its terms (where checked: Anthropic, OpenAI,
Google, OpenRouter), and is asked once per studyset and assistant: the
agreement is kept in the person's sealed settings (schema 13,
privateAgreements, folded only where both rows hold it), shown in the
studyset's privacy dialog with Take back, and marked on the folded
button while it holds. Follow-ups and Try again ask again once taken
back, as the scope keeps where the parts came from (partsFrom). No
warning for an own assistant on this machine (loopback or localhost,
halkyon_llm's LlmEndpoint.onThisMachine); the local network may be
shared.

Texts that step 3 made untrue: the consent sheet now says what an
assistant looks up goes too and that conversations are kept encrypted
for the person's devices; the privacy dialogs no longer mention
showing a studyset to Claude; the privacy page says what is looked up
and when a private studyset goes.

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/lib/src/instance/privacy_page.dart

@@ -258,7 +258,8 @@ final _english = _Words(
           '${images ? ', which reads images you add' : ''}.',
   whatGoes:
       'Only what you send from the app goes, once you agreed to it there: '
-      'your question and what you pick of what it is about. It passes through '
+      'your question, what you pick of what it is about, and what the '
+      'assistant looks up where you let it. It passes through '
       'the instance on its way to the provider; the instance keeps none of '
       'it, and the provider’s own terms apply to it. Each request carries an '
       'ID the instance makes for you, which tells the provider nothing of who '
@@ -341,7 +342,8 @@ final _german = _Words(
           '${images ? ', das Bilder liest, die du hinzufügst' : ''}.',
   whatGoes:
       'Es geht nur, was du aus der App sendest, nachdem du dort zugestimmt '
-      'hast: deine Frage und was du davon auswählst, worum es geht. Es geht '
+      'hast: deine Frage, was du davon auswählst, worum es geht, und was der '
+      'Assistent nachschlägt, wo du es lässt. Es geht '
       'auf dem Weg zum Anbieter durch die Instanz; die Instanz bewahrt nichts '
       'davon auf, und für den Anbieter gelten seine eigenen Bedingungen. Jede '
       'Anfrage trägt eine ID, die die Instanz für dich bildet und die dem '