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_logs.py

@@ -219,11 +219,11 @@ def _client() -> TestClient:
             raise HTTPException(status_code=400, detail={"code": "bad_cursor"})
         return {"ok": True}
 
-    @app.get("/api/messages/unread_count")
+    @app.get("/api/me/notifications/unread_count")
     def _unread():
         return {"count": 0}
 
-    @app.post("/api/messages/unread_count")
+    @app.post("/api/me/notifications/unread_count")
     def _unread_write():
         return {"ok": True}
 
@@ -337,11 +337,11 @@ def test_a_polled_read_is_debug_a_write_to_the_same_route_is_not(sink):
     http = logging.getLogger("siftlode.http")
     http.setLevel(logs.TRACE)
     client = _client()
-    r = client.get("/api/messages/unread_count")
+    r = client.get("/api/me/notifications/unread_count")
     assert sink.objects()[-1]["level"] == "DEBUG"
     # ...and says so, for the browser's copy of the line (frontend lib/http.ts).
     assert r.headers["X-Log-Quiet"] == "1"
-    r = client.post("/api/messages/unread_count")
+    r = client.post("/api/me/notifications/unread_count")
     assert sink.objects()[-1]["level"] == "INFO"
     assert "X-Log-Quiet" not in r.headers
     assert client.get("/api/videos/abc").status_code == 200