chore(spec): record PUBLIC_FORM_SERVER_MANAGED_FIELDS in the api-surface snapshot (#3022)

The lint.yml api-surface gate flags any public-API change; the new export is
the intentional addition from the #3022 fix, so regenerate and commit the
snapshot per the gate's instruction.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lr7QwD4Fx9KYkLH1xDMwEo

Author: claude

packages/spec/api-surface.json

@@ -3976,6 +3976,7 @@
     "OwnerSharingRuleSchema (const)",
     "PLATFORM_CAPABILITIES (const)",
     "PLATFORM_CAPABILITY_NAMES (const)",
+    "PUBLIC_FORM_SERVER_MANAGED_FIELDS (const)",
     "PermissionSet (type)",
     "PermissionSetInput (type)",
     "PermissionSetSchema (const)",