feat(seeder): dev event_registration schema with draft + submitted submissions exercising FORM-02 (§31.10)

Sprint 0.5. Extends FormBuilderDevSeeder (additive) so that after
`migrate:fresh --seed` the dev org has:

- one published public-token-enabled event_registration schema anchored
  to the primary festival (Echt Feesten 2026) with a curated 5-field
  set (HEADING / SELECT / CHECKBOX_LIST / TAG_PICKER / TEXTAREA) —
  mirrors the subset Bert needs to eyeball via the portal and verify
  §31.10 sync with;
- one draft submission (partial fill: shirtmaat + dieetwensen) for the
  first approved person with user_id — the TAG_PICKER is deliberately
  absent so this submission does NOT fire the listener;
- one submitted submission for the next approved person, with
  TAG_PICKER values = the first 3 active person_tags by sort_order.
  The submission is pushed through FormSubmissionService::submit so
  FormSubmissionSubmitted fires, SyncTagPickerSelectionsOnSubmit runs,
  and user_organisation_tags receives 3 self_reported rows.

Queue-connection contract: production runs QUEUE_CONNECTION=redis, so
the listener would queue and not execute before the seeder returns.
The seeder temporarily flips queue.default to sync for the submit()
call so Bert sees the synced tags immediately after `--seed`.

Console output matches the Sprint 0.5 spec: public URL for GET-testing
+ a line naming the submitter and the sync result count.

Wired from DevSeeder::seedEchtFeesten() behind an
app()->environment('local', 'testing', 'development') guard (belt-and-
suspenders on top of DatabaseSeeder's existing local gate).

Collateral fix: FormSubmissionService::submit() stored signed fractional
seconds into the unsigned `submission_duration_seconds` column. Carbon
3's diffInSeconds returns signed floats when `opened_at` is earlier than
now, which MySQL rejects. Wrapped with abs() + int cast. No test
expectations relied on the sign so 857 tests remain green.

Verified via tinker after `migrate:fresh --seed`:
  fields_count = 5, submissions_count = 2 (1 draft + 1 submitted),
  values on submitted = 4, self_reported tags for submitter = 3,
  PublicFormSchemaResource returns all 5 fields on the public token.

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

api/app/Services/FormBuilder/FormSubmissionService.php

@@ -109,7 +109,9 @@ final class FormSubmissionService
             }
 
             if ($submission->opened_at !== null) {
-                $submission->submission_duration_seconds = now()->diffInSeconds($submission->opened_at);
+                // abs + int cast: Carbon's diffInSeconds returns signed fractional
+                // seconds, and the column is unsignedInteger.
+                $submission->submission_duration_seconds = (int) abs(now()->diffInSeconds($submission->opened_at));
             }
 
             $submission->save();