Fix resource.json timestamp: strip milliseconds for Ignition compat

Ignition's JSON parser can't handle ISO timestamps with milliseconds
(2026-03-30T19:31:53.623Z). Strip to seconds (2026-03-30T19:31:53Z).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

svelte-app/src/lib/export.ts

@@ -585,7 +585,7 @@ export async function deployToIgnition() {
       lastModificationSignature: signature,
       lastModification: {
         actor: 'admin',
-        timestamp: new Date().toISOString(),
+        timestamp: new Date().toISOString().replace(/\.\d{3}Z$/, 'Z'),
       },
     },
   }, null, 2);