fix(#20): heid-code-review fixups — stale docstring + None-cursor test (slice-6)

Panel (Gróa + Hulda + Regin): 3/3 no drift — the admin adapter honors the contract
(route map, re-wrap/degrade, error-map ORDER, admin_auth-on-client, INV-CUT-1).
Only minor doc/test looseness, both fixed:

- Stale docstring: `_session_bifrost_endpoint` still said "the wrapper overrides the
  Authorization header with it" — corrected to "rides on the wt client's admin_auth"
  (slice-6 moved admin auth off the per-call header; line 79 already said the new way).
- Test-gap: the admin-stream ConnectionDropped test only exercised the cursor-set case;
  added the connect-time None-cursor case (ConnectionDropped(None) → last_seen_sse_id
  None) to back the map's "both cursor shapes" claim.

Not acted on: `admin_key`→`admin_auth` unit assertion (the SDK's use of admin_auth is
SDK-internal/private — out of scope per "assess use, not definitions"; the LIVE SMOKE
already proved the wiring end-to-end). Hulda's "web endpoints under-tested" flag was
source-VOIDED by Heid: those endpoints ARE covered in test_web_server.py, which wasn't
in the consult embed (excerpt-elides-tests trap).

Suite 491 green; ruff clean. Docs + test only — no version bump (SemVer skip rule).

tests/test_wt.py

@@ -1212,10 +1212,18 @@ class TestStreamAdminEventsWt:
             await _drain(stream_admin_events(_wtad(fake)))
         assert ei.value.status == 502
 
-    async def test_connection_dropped_maps_and_carries_cursor(self) -> None:
-        # Both a connect-time failure (cursor None) and a mid-stream drop / resumable
-        # EOF (cursor set) surface as ConnectionDropped → SseConnectionDropped.
+    async def test_connection_dropped_carries_cursor(self) -> None:
+        # A mid-stream drop / resumable EOF carries the resume cursor.
         fake = _FakeAdmin(stream_error=wtsdk.ConnectionDropped("42"))
         with pytest.raises(SseConnectionDropped) as ei:
             await _drain(stream_admin_events(_wtad(fake)))
         assert ei.value.last_seen_sse_id == "42"
+
+    async def test_connection_dropped_none_cursor_connect_time(self) -> None:
+        # A connect-time transport failure surfaces as ConnectionDropped(None) →
+        # SseConnectionDropped(last_seen_sse_id=None) (the map's other cursor shape;
+        # heid-code-review slice-6 test-gap).
+        fake = _FakeAdmin(stream_error=wtsdk.ConnectionDropped(None))
+        with pytest.raises(SseConnectionDropped) as ei:
+            await _drain(stream_admin_events(_wtad(fake)))
+        assert ei.value.last_seen_sse_id is None