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-conversation/tests/chat-code-subcalls.spec.tsx

@@ -78,7 +78,7 @@ async function bench(snapshot: ConversationSnapshot) {
   const session = createSnapshotStore<ConversationSnapshot>(snapshot)
   const list = createSnapshotStore<SessionListState>({
     ids: [SID],
-    byId: { [SID]: { id: SID, title: 'S', displayTitle: 'S', running: false, blank: false, updatedAt: 1 } },
+    byId: { [SID]: { id: SID, title: 'S', displayTitle: 'S', running: false, waitingApproval: false, blank: false, updatedAt: 1 } },
     current: SID,
     phase: 'ready',
   })