feat!: remove direct messaging (chat)

E2EE direct messages, the chat dock, the Messages module, the message
WebSocket and its realtime registry, and the messages / message_keys
tables (migration 0097; the downgrade restores the empty schema). Prod
held two welcome notes, no message between people and one key — never
used (owner decision, E34). WebSocket now has no owner module: the lint
bans it everywhere. Privacy policy updated: it no longer promises E2EE
for a feature that is gone.

backend/tests/test_collation.py

@@ -221,30 +221,13 @@ def _others(db, n_offset: int = 0) -> list[User]:
     return users
 
 
-def test_the_share_and_message_recipients_are_in_the_readers_alphabet(
-    db, monkeypatch, override_dep
-):
-    from app.models import MessageKey
-
+def test_the_share_recipients_are_in_the_readers_alphabet(db, monkeypatch, override_dep):
     user = _user(db, "hu")
-    others = _others(db)
-    db.add_all(
-        MessageKey(
-            user_id=u.id,
-            public_key="k",
-            wrapped_private_key="w",
-            salt="s",
-            wrap_iv="i",
-            key_check="c",
-        )
-        for u in others
-    )
+    _others(db)
     db.commit()
     client = _client(db, user, monkeypatch, override_dep)
     emails = [r["email"] for r in client.get("/api/downloads/recipients").json()]
     assert emails == [f"{w.lower()}@example.com" for w in HU]
-    names = [r["name"] for r in client.get("/api/messages/users").json()]
-    assert names == HU
 
 
 def test_the_blocked_channels_are_in_the_readers_alphabet(db, monkeypatch, override_dep):