feat(uat-batch-13): activity feed resolves user UUIDs to display names

Audit-log rows with user-FK diffs (assignedTo, ownerId, reassignedTo,
createdBy, addedBy, changedBy, transferredBy) previously rendered the
raw user UUID in the activity feed (e.g. "→ mEcsLxo5kyFMyhbOSehxJjY…").
Same gap on the row's actor — the rep had no idea who did what.

- getRecentActivity collects all userIds referenced by either the row's
  actor (auditLogs.userId) or by user-FK diff values, then bulk-fetches
  user_profiles in a single query. Output rows now carry an
  `actorName` field and have their `oldValue`/`newValue` swapped for
  display names on user-FK fields.
- Unknown / deleted users fall back to "Unknown user (#short-uuid)" so
  the audit trail stays useful for forensics.
- ActivityItem client type extended with `actorName`. Existing
  consumers still read the raw `userId` for forensics + deep-link.

tsc clean. 1419/1419 vitest pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/dashboard/activity-feed.tsx

@@ -28,7 +28,14 @@ interface ActivityItem {
    *  underlying entity still exists. Falls back to the id prefix in the UI. */
   label: string | null;
   userId: string | null;
+  /** Server-resolved actor display name (from user_profiles). When null,
+   *  the actor row no longer exists — render falls back to a "Unknown
+   *  user" sentinel rather than the raw UUID prefix. */
+  actorName: string | null;
   fieldChanged: string | null;
+  /** For user-FK diff rows (assignedTo, ownerId, etc.) the service
+   *  already replaces these with display names. Non-user-FK rows pass
+   *  through verbatim. */
   oldValue: unknown;
   newValue: unknown;
   metadata: Record<string, unknown> | null;