Preserve deleted server history

Retain historical server identities, results, and evidence after deletion. Mark archived entries as Deleted and prevent old work from targeting servers that reuse the same name.

Fixes #16.

src/lib/watchdog.ts

@@ -4,6 +4,7 @@ export type WatchdogState = 'open' | 'recovering' | 'attention' | 'resolved' | '
 export interface WatchdogIncident {
     id: string;
     server: string;
+    server_deleted_at?: string | null;
     kind: 'health' | 'drift';
     state: WatchdogState;
     summary: string;