refactor(web): drop the permission RPC pair and turn-anchoring machinery

The session.permissions/setPermission unary pair, the PermissionOption wire
DTO, the client Session wrappers, and the fixture/fake mirrors all leave the
wire: the read side moves to the 'permissions' session projection and the
write side moves to the /permission command in follow-up commits, so the
web protocol gains no permission methods at all.

The pendingSwitches + prompt-submit flush + hasOpenTurn move also goes.
Knob events no longer need turn enclosure: the persistence scanner keeps
standalone events after the last turn/end as part of the preserved prefix
(remove-synthetic-log-only-turns), none of the three knob invariants demand
an open turn, and the setters append bare events. An idle switch commits
immediately; hasOpenTurn stays a user-approval private fold (its audit pair
is the one contract that still requires enclosure).

The old PermissionSelect chip and its mount-time fetch die with the RPCs
(the resident composer broke the mount-once assumption); the projection-fed
replacement lands with the Access seat swap.

packages/client/ui-trajectory/tests/views.spec.tsx

@@ -149,8 +149,6 @@ function mount(slots: SlotsService, nodes: ConversationSnapshot['nodes'] = NODES
       inputActions={{ setDraft: vi.fn(), submit: vi.fn() }}
       bindDraftMirror={() => () => {}}
       open={vi.fn()}
-      permissions={() => Promise.resolve(null)}
-      setPermission={() => Promise.resolve(null)}
     />,
   )
 }