feat(migrate): daemon-update prompt + migrate-to-seed UX polish + i18n

Fixes the Windows migrate-to-seed failure (the old bundled daemon lacked
z_exportmnemonic) and rounds out the flow:

- seed_wallet_creator: actionable "daemon too old" message instead of the
  raw "Method not found" RPC error.
- Startup daemon-update prompt: if the wallet bundles a newer node than the
  installed one, offer to update it (once per version, keyed on a new
  daemon_update_prompted_size setting; never silently clobbers a custom
  node). "Install bundled" now also works when attached to an external /
  leftover daemon (RPC-stops it, then swaps + restarts).
- Migrate-to-seed Intro pre-flight: detect an already-mnemonic wallet
  (offer backup instead), an old daemon, or a locked/disconnected wallet
  before offering to create anything.
- No-funds path: a zero-balance wallet can adopt the new seed wallet
  directly (behind an acknowledgement checkbox) instead of a dead sweep.
- Loading spinners on the Working/Sweeping/Adopting steps; sweep coverage
  for the new intro / no-funds surfaces.
- Translations for all 18 new strings across 8 languages (+ rebuilt CJK
  subset font).

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

src/config/settings.cpp

@@ -200,6 +200,7 @@ bool Settings::load(const std::string& path)
         }
         loadScalar(j, "wizard_completed", wizard_completed_);
         loadScalar(j, "seed_backup_reminded", seed_backup_reminded_);
+        loadScalar(j, "daemon_update_prompted_size", daemon_update_prompted_size_);
         loadScalar(j, "seed_migration_pending", seed_migration_pending_);
         loadScalar(j, "seed_migration_dest", seed_migration_dest_);
         loadScalar(j, "seed_migration_temp_dir", seed_migration_temp_dir_);
@@ -438,6 +439,7 @@ bool Settings::save(const std::string& path)
     }
     j["wizard_completed"] = wizard_completed_;
     j["seed_backup_reminded"] = seed_backup_reminded_;
+    j["daemon_update_prompted_size"] = daemon_update_prompted_size_;
     j["seed_migration_pending"] = seed_migration_pending_;
     j["seed_migration_dest"] = seed_migration_dest_;
     j["seed_migration_temp_dir"] = seed_migration_temp_dir_;