Store the person uuid the master issues, so renames keep our identity

The welcome now carries a personId; it lands in the instance_id setting
and rides on every hello and HTTP report from then on. The master keys
the person by that uuid, so changing instance_name moves our history to
the new name instead of starting a stranger. Read-only in Settings on
purpose — editing it by hand would detach this machine from its person.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/master-protocol.ts

@@ -106,10 +106,13 @@ export type Command =
     | { kind: 'report-now' };
 
 export type MasterMessage =
-    | { type: 'welcome' }
+    /** personId is the person's stable uuid; the instance stores it and
+     *  presents it on later hellos, which is what makes a rename follow the
+     *  person. */
+    | { type: 'welcome'; personId?: string }
     | { type: 'command'; id: string; command: Command };
 
 export type InstanceMessage =
-    | { type: 'hello'; instance: string; capabilities: InstanceCapabilities }
+    | { type: 'hello'; instance: string; id?: string; capabilities: InstanceCapabilities }
     | { type: 'report'; firms: FirmStats[]; scheduler: SchedulerState; capabilities?: InstanceCapabilities }
     | { type: 'ack'; id: string; ok: boolean; result?: unknown; error?: string };