feat: cover seedlings (plantón) in copy + legal, backup cadence, server picker

Beta-tester feedback triage. The data model already had LotType.seedling as
first class; the gaps were copy and UX.

- Seedlings/plantones: broaden landing hero (EN/ES), in-app legal notice, and
  all legal texts (site + docs masters) from seeds-only to "seeds and
  seedlings", with a live-plant phytosanitary/transport caveat. Seeds stay the
  hero — targeted, not a blanket rename.
- Backups: settings line now states the 7-day cadence explicitly; cadence lives
  in AutoBackupService.backupInterval as the single source for text and schedule.
- Community servers: replace the manual wss:// text box with a checklist of the
  known servers (defaults visible/toggleable) plus an "add server" affordance
  with basic validation. No jargon in the UI.

i18n across en/es/pt/fr/de/ast (ja falls back). Tests updated + a new
server-picker widget test.

apps/app_seeds/lib/ui/backup_section.dart

@@ -357,8 +357,9 @@ class _AutoBackupTileState extends State<_AutoBackupTile> {
       future: _lastBackup,
       builder: (context, snapshot) {
         final last = snapshot.data;
+        final days = AutoBackupService.backupInterval.inDays;
         final subtitle = last == null
-            ? t.backup.autoBackupNone
+            ? t.backup.autoBackupNone(days: days)
             : t.backup.autoBackupLast(
                 // Format via the Localizations locale, not the raw app locale:
                 // Asturian (`ast`) has no `intl` date symbols and would throw,
@@ -366,6 +367,7 @@ class _AutoBackupTileState extends State<_AutoBackupTile> {
                 date: DateFormat.yMMMd(
                   Localizations.localeOf(context).languageCode,
                 ).format(last),
+                days: days,
               );
         return ListTile(
           leading: const Icon(Icons.shield_outlined),