fix(plugin-audit): write explicit ISO timestamp on sys_activity rows

The sys_activity.timestamp column declares defaultValue: 'NOW()' as a
framework convention, but the SQL driver currently stores it as a
literal string instead of translating it to CURRENT_TIMESTAMP, so every
audit row that relied on the default leaked the string 'NOW()' into the
record and the timeline rendered 'Invalid Date'.

Set timestamp explicitly to new Date().toISOString() in the audit
writer so we don't depend on the driver-side resolution. Filed
separately as M11 — the broader 'NOW()' default-value sweep across
platform-objects (sys-comment, sys-notification, sys-presence, …) still
needs the driver fix.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: hotlong

packages/plugins/plugin-audit/src/audit-writers.ts

@@ -192,6 +192,10 @@ export function installAuditWriters(engine: any, packageId = 'com.objectstack.au
 
     const activityRow: Record<string, any> = {
       type: activityTypeFor(action),
+      // Explicit ISO timestamp — `defaultValue: 'NOW()'` on the column
+      // isn't resolved by every driver and would otherwise leak the
+      // literal string "NOW()" into the row.
+      timestamp: new Date().toISOString(),
       summary,
       actor_id: userId ?? null,
       object_name: ctx.object,