gate group chats for under-18 users

Per the group chats spec, users under 18 cannot be added to or participate in
group chats. This wires up the client-side half:

- expose isUnder18 flag from the AA context (conservative default when
  birthdate is unknown)
- new restrictGroupChatSettings helper that writes
  allowGroupInvites: 'none' to the chat actor declaration, called on signup
  and on birthdate-update when the user is under 18
- hide the 'New group chat' entry in InitiateChatFlow for under-18 users
- lock the 'Allow group chat invites from' toggle to 'none' for under-18 in
  chat settings, with explanatory copy
- pass kind: 'direct' to listConvos for under-18 users so groups don't show
  in the requests inbox or count toward the unread/requests badges

src/state/queries/messages/restrictChatSettings.ts

@@ -3,7 +3,10 @@ import {type ChatBskyActorDeclaration} from '@atproto/api'
 
 import {networkRetry} from '#/lib/async/retry'
 import {logger} from '#/logger'
-import {setOtherRequiredDataActorDeclarationCache} from '#/ageAssurance/data'
+import {
+  getOtherRequiredDataFromCache,
+  setOtherRequiredDataActorDeclarationCache,
+} from '#/ageAssurance/data'
 
 /**
  * Helper to update the chat settings record.
@@ -37,3 +40,44 @@ export async function restrictChatSettings({
     logger.error(`restrictChatSettings: failed to set chat declaration`)
   }
 }
+
+/**
+ * Locks the user out of being added to group chats by setting
+ * `allowGroupInvites: 'none'` on the chat actor declaration. Used for under-18
+ * users, who per spec cannot participate in group chats.
+ *
+ * Preserves the existing `allowIncoming` value if one is cached, otherwise
+ * defaults to 'following' (the lexicon default) since the field is required.
+ */
+export async function restrictGroupChatSettings({
+  agent,
+  did,
+}: {
+  agent: AtpAgent
+  did: string
+}): Promise<void> {
+  const cached = getOtherRequiredDataFromCache({did})?.actorDeclaration
+  if (cached?.allowGroupInvites === 'none') return
+
+  try {
+    const record: ChatBskyActorDeclaration.Main = {
+      $type: 'chat.bsky.actor.declaration',
+      allowIncoming: cached?.allowIncoming ?? 'following',
+      allowGroupInvites: 'none',
+    }
+    await networkRetry(3, () =>
+      agent.com.atproto.repo.putRecord({
+        repo: did,
+        collection: 'chat.bsky.actor.declaration',
+        rkey: 'self',
+        record,
+      }),
+    )
+    setOtherRequiredDataActorDeclarationCache({
+      did,
+      actorDeclaration: record,
+    })
+  } catch {
+    logger.error(`restrictGroupChatSettings: failed to set chat declaration`)
+  }
+}