chore(contextual): purge residual floating WsFrame defs + output_formatter branch

After M6.5 deletion of run_floating_stream and the frame dispatch,
WsFrameType.floating_request/floating_domain, WsFloatingRequest,
WsFloatingDomain, WsFloatingScope, WsDomain, and the StreamFormatter's
floating_domain branch were left as dead protocol surface. Remove them,
along with the corresponding test cases in test_schemas_v3.py and
test_output_formatter.py.

tests/test_output_formatter.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 import pytest
 
 from app.core.output_formatter import StreamFormatter
-from app.schemas import WsFloatingDomain, WsStreamEnd, WsStreamStart, WsStreamText
+from app.schemas import WsStreamEnd, WsStreamStart, WsStreamText
 
 
 async def _stream(*events: tuple[str, object]):
@@ -36,29 +36,6 @@ async def test_stream_formatter_text_stream() -> None:
     assert isinstance(frames[-1], WsStreamEnd)
 
 
-@pytest.mark.asyncio
-async def test_stream_formatter_floating_domain_first() -> None:
-    formatter = StreamFormatter(request_id="req-2")
-    frames = await _collect(
-        formatter,
-        _stream(
-            (
-                "floating_domain",
-                {"type": "node", "id": "n-1", "section": None},
-            ),
-            ("token", "Summary"),
-        ),
-    )
-
-    assert isinstance(frames[0], WsFloatingDomain)
-    assert frames[0].domain.type == "node"
-    assert frames[0].domain.id == "n-1"
-    assert isinstance(frames[1], WsStreamStart)
-    assert isinstance(frames[2], WsStreamText)
-    assert frames[2].chunk == "Summary"
-    assert isinstance(frames[-1], WsStreamEnd)
-
-
 @pytest.mark.asyncio
 async def test_stream_formatter_ignores_unknown_events() -> None:
     formatter = StreamFormatter(request_id="req-3")