Fix fresh-install migration blocker + add preflight, seed admin, first-run endpoints

Validated a clean install on MySQL 5.6 end to end and fixed the blockers.

- migrations/env.py: force alembic_version.version_num to VARCHAR(128) in its
  own committed connection before running migrations. It was VARCHAR(32); the
  revision id 7d02_widen_notification_employee_cols (37 chars) truncated, so the
  next migration's version bump matched 0 rows and `flask db upgrade` died at
  7d03 on a fresh DB. Now upgrades run clean to head.
- flask db-utils preflight: checks Python, required env, DB connectivity, and
  the MySQL 5.6 utf8mb4 index flags (innodb_large_prefix/Barracuda) - the 767
  prerequisite - and prints exact fixes. Exits non-zero on blockers.
- flask seed admin --username --email [--password]: real first-admin command
  (generates + prints a password once). The docs referenced it but only the
  dev-only test-user existed.
- setup endpoints for a UI-driven first run: /setup/needs-admin,
  /setup/create-admin (guarded to zero-users), /setup/seed-reference.
- Wizard: drop the PC-access-domain question (always .device.geaerospace.net);
  the setting keeps its default.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/api/index.js

@@ -773,6 +773,15 @@ export const pluginsApi = {
 }
 
 export const setupApi = {
+  needsAdmin() {
+    return api.get('/setup/needs-admin')
+  },
+  createAdmin(data) {
+    return api.post('/setup/create-admin', data)
+  },
+  seedReference() {
+    return api.post('/setup/seed-reference')
+  },
   seedStarter() {
     return api.post('/setup/seed-starter')
   },

frontend/src/views/SetupWizard.vue

@@ -25,10 +25,6 @@
             <label>Site base URL <span class="hint">(blank = use the browsing origin)</span></label>
             <input v-model="form.site_base_url" type="url" class="form-control" placeholder="https://shopdb.example.net" />
           </div>
-          <div class="form-group">
-            <label>PC access domain <span class="hint">(for remote-access links)</span></label>
-            <input v-model="form.pc_access_domain" type="text" class="form-control" placeholder="device.geaerospace.net" />
-          </div>
         </div>
 
         <!-- Plugins -->
@@ -168,7 +164,7 @@ const step = ref(0)
 const current = computed(() => steps[step.value])
 
 const form = ref({
-  facility_name: '', site_base_url: '', pc_access_domain: '',
+  facility_name: '', site_base_url: '',
   map_width: null, map_height: null,
 })
 const plugins = ref([])
@@ -226,13 +222,13 @@ const envLines = computed(() => {
 
 // Which settings each step owns, so Next only saves what changed on that step.
 const stepSettings = {
-  site: ['facility_name', 'site_base_url', 'pc_access_domain'],
+  site: ['facility_name', 'site_base_url'],
   map: ['map_width', 'map_height'],
 }
 
 onMounted(async () => {
   // Load current values for the settings the wizard edits.
-  const keys = ['facility_name', 'site_base_url', 'pc_access_domain', 'map_width', 'map_height']
+  const keys = ['facility_name', 'site_base_url', 'map_width', 'map_height']
   for (const key of keys) {
     try {
       const response = await settingsApi.get(key)