chore(web): drop plan RPC residue and stale carriers after merge

Sweep the silently auto-merged leftovers of the superseded #587 wire layer:
the PlanModeState interface and planMode/setPlanMode entries in the sessions
API and rpc map, the fixture plan RPC spec, the composer.controls README
paragraph and spec assertions, the old-format plan-mode snapshot, and the
two Agent Notes written against the RPC design (to be rewritten for the
projection reattachment). ChatView/PendingCard keep the approval-only
pending rendering; QuestionComposer improvements ride along unchanged.

packages/client/ui-conversation/tests/chat-apply.spec.tsx

@@ -91,7 +91,6 @@ describe('apply wiring', () => {
     // Declaring is claiming: the chat entry's registration put the hole on
     // the ledger with the contract's kind/scope.
     expect(b.slots.spec('conversation.chat.toolview')).toEqual({ kind: 'keyed', scope: 'session' })
-    expect(b.slots.spec('conversation.composer.controls')).toEqual({ kind: 'list', scope: 'session' })
   })
 
   it('occupies the slots + the ring; session entries share one store handle', async () => {
@@ -133,7 +132,6 @@ describe('apply wiring', () => {
     expect(b.slots.entries('conversation.view')).toHaveLength(0)
     expect(b.slots.entries('conversation.chat.toolview')).toHaveLength(0)
     expect(b.slots.spec('conversation.chat.toolview')).toBeUndefined()
-    expect(b.slots.spec('conversation.composer.controls')).toBeUndefined()
     expect(b.slots.entries('details')).toHaveLength(0)
     expect(b.ctx.get('conversation')).toBeUndefined()
   })