feat: command.execute returns the lifecycle pairing id ({matched, commandId?})

CommandService.execute now returns a CommandExecution — the normalized
result plus the commandId minted for its command/run/command/done records —
and the wire admission value carries commandId exactly when matched, so the
issuing client can correlate its RPC acknowledgment with the flow node the
lifecycle events produce. apiproxy api/schema/handler, the connection
fixture, and the TUI/plan/goal consumers follow the new shape.

packages/client/connection/src/client/fixture.ts

@@ -830,7 +830,7 @@ export function createFixtureApi(options: FixtureOptions = {}): ApiProxy {
         const commandId = `fx-cmd-${logOf(id).length}`
         append(id, { type: 'command/run', data: { commandId, name, args, source: { kind: 'user' } } })
         append(id, { type: 'command/done', data: { commandId, kind: 'success', ...text === '' ? {} : { text } } })
-        return ok(request, { matched: true as const })
+        return ok(request, { matched: true as const, commandId })
       },
     },
     skills: {