refactor(schema): migrate eleven pivot/EAV tables to ULID per addendum Q1

Retires the "integer AI PK for join performance" exception documented
in earlier migrations and SCHEMA.md §3.5.11 Rule 1. Every business and
pivot table now uses ULID primary keys, per
/dev-docs/ARCH-CONSOLIDATION-ADDENDUM-2026-04-24.md Q1.

Tables migrated (WS-1 A-01 through A-11):
- Pure pivots: organisation_user, event_user_roles, crowd_list_persons,
  event_person_activations
- Model-backed: user_organisation_tags, person_section_preferences,
  mfa_backup_codes, mfa_email_codes, form_submission_section_statuses,
  form_values, form_value_options

Migration pattern: one new migration per table (plus one combined for
the form_values / form_value_options FK pair), timestamped today,
dropping + recreating with the new ULID PK. Pre-launch — no backfill
required. Original migrations remain in place; the new migrations
apply in timestamp order for a clean schema history.

Pivot model correction (addendum drift):
The addendum's "no model required for pure pivots" reading did not
account for Laravel's BelongsToMany::attach() — it cannot auto-generate
a pivot ULID without a Pivot subclass. Minimal Pivot classes under
app/Models/Pivots/ (OrganisationUser, EventUserRole, CrowdListPerson,
EventPersonActivation) carry HasUlids so attach() works. The six
belongsToMany relations (User.organisations / .events, Organisation.users,
Event.users, CrowdList.persons, Person.crowdLists) now ->using(...) the
appropriate Pivot class. DB::table()->insert() on event_person_activations
in DevSeeder populates the ULID inline via Str::ulid(). FormValueObserver
uses bulk FormValueOption::insert() which bypasses model events — ULIDs
are now generated inline there too.

Docs:
- SCHEMA.md §3.5.11 Rule 1 rewritten to mandate ULID on pivots too, with
  legacy note citing the addendum.
- All eleven table entries updated from "int AI PK" to "ULID PK" with
  addendum Q1 references.
- form_values and form_submission_section_statuses prose blocks updated
  to drop the retired ARCH §4.4 / "high-volume pivot" rationale.
- form_value_options.form_value_id column type corrected from
  "int FK" to "ULID FK".

Tests: tests/Feature/Schema/UlidPrimaryKeyTest.php covers HasUlids trait
presence, ULID shape + 26-char Crockford pattern, Route::bind resolution,
distinct + sortable pivot ULIDs, attach() auto-generation on pure pivots,
and the A-10/A-11 FK chain. 10 tests / 28 new assertions. Full suite:
977 passed (2662 assertions).

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

api/app/Models/Pivots/CrowdListPerson.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models\Pivots;
+
+use Illuminate\Database\Eloquent\Concerns\HasUlids;
+use Illuminate\Database\Eloquent\Relations\Pivot;
+
+final class CrowdListPerson extends Pivot
+{
+    use HasUlids;
+
+    protected $table = 'crowd_list_persons';
+
+    public $incrementing = false;
+
+    protected $keyType = 'string';
+}

api/app/Models/Pivots/EventPersonActivation.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models\Pivots;
+
+use Illuminate\Database\Eloquent\Concerns\HasUlids;
+use Illuminate\Database\Eloquent\Relations\Pivot;
+
+final class EventPersonActivation extends Pivot
+{
+    use HasUlids;
+
+    protected $table = 'event_person_activations';
+
+    public $incrementing = false;
+
+    protected $keyType = 'string';
+}

api/app/Models/Pivots/EventUserRole.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models\Pivots;
+
+use Illuminate\Database\Eloquent\Concerns\HasUlids;
+use Illuminate\Database\Eloquent\Relations\Pivot;
+
+final class EventUserRole extends Pivot
+{
+    use HasUlids;
+
+    protected $table = 'event_user_roles';
+
+    public $incrementing = false;
+
+    protected $keyType = 'string';
+}

api/app/Models/Pivots/OrganisationUser.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models\Pivots;
+
+use Illuminate\Database\Eloquent\Concerns\HasUlids;
+use Illuminate\Database\Eloquent\Relations\Pivot;
+
+final class OrganisationUser extends Pivot
+{
+    use HasUlids;
+
+    protected $table = 'organisation_user';
+
+    public $incrementing = false;
+
+    protected $keyType = 'string';
+}