refactor: command.execute degrades to pure admission; composer notice channel retired

The wire response now carries only the matched bit — CommandExecuteResult
is deleted from the api, schema, and client mirrors (pre-release, no shim);
outcomes ride the durably logged command/run/command/done pair broadcast on
the mux stream and render as flow nodes. ui-command's runDetached→noticeFor
outcome routing is retired: admitted commands surface nothing through the
composer, while admission misses (matched:false, syntax feedback) and
transport failures keep their immediate notice. The connection fixture
mirrors the host: an admitted command appends the lifecycle pair to the
session log instead of returning result text.

packages/host/apiproxy/src/api/index.ts

@@ -28,7 +28,7 @@ export interface ApiProxy {
 export type { HistoryEntry, SessionProjectionsBlock, SessionsApi, SessionSummary } from './sessions.ts'
 export type { HostApi } from './host.ts'
 export type { WorkspaceApi, WorkspaceId, WorkspaceView } from './workspace.ts'
-export type { CommandsApi, CommandDescriptor, CommandExecuteResult } from './commands.ts'
+export type { CommandsApi, CommandDescriptor } from './commands.ts'
 export type { SkillsApi, SkillEntry } from './skills.ts'
 export type { EventsApi, MuxFrame, HostFrame, ToolCallView, ToolEventView, ToolResultView } from './events.ts'
 export type { ApprovalResponsePayload } from './approvals.ts'