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/util/i18n.cpp

@@ -255,6 +255,22 @@ void I18n::loadBuiltinEnglish()
         strings_["mig_title"] = "Migrate to a seed wallet";
         strings_["mig_intro"] = "This creates a brand-new wallet backed by a 24-word seed phrase, in an isolated node, so you can move your funds into it. Your current wallet is NOT touched and NO funds move in this step — you'll back up the new seed first, then sweep your funds into it as a separate, confirmed step.";
         strings_["mig_create"] = "Create seed wallet";
+        // Intro pre-flight (checking the current wallet before offering to migrate)
+        strings_["mig_precheck_checking"] = "Checking your wallet";
+        strings_["mig_already_mnemonic"] = "Your wallet already has a 24-word seed phrase — there's nothing to migrate. Just back it up and keep the words somewhere safe.";
+        strings_["mig_backup_instead"] = "Back up seed phrase";
+        strings_["mig_daemon_too_old"] = "Your DragonX node is too old to create a seed wallet — it lacks the mnemonic support this needs. Update the node (Settings → NODE & SECURITY → Install bundled, or Check for updates), then try again.";
+        strings_["mig_not_connected"] = "Connect to your node first, then reopen this to migrate.";
+        strings_["mig_unlock_to_migrate"] = "Unlock your wallet first, then reopen this to migrate.";
+        strings_["mig_check_failed"] = "Couldn't check your wallet. Make sure it's unlocked and connected, then re-check.";
+        strings_["mig_recheck"] = "Re-check";
+        // Sweep step: balance still loading / no funds to move
+        strings_["mig_checking_balance"] = "Checking your balance";
+        strings_["mig_no_funds"] = "Your wallet has no funds to migrate. You can adopt the new seed wallet directly — it replaces your current (empty) wallet with the seed-backed one. Your old wallet is still moved aside to a timestamped backup, just in case.";
+        strings_["mig_adopt_now"] = "Adopt seed wallet";
+        strings_["mig_nofunds_confirm"] = "I understand this replaces my current wallet with the new seed wallet";
+        // Adopting step note (shown under the spinner while the node restarts + rescans)
+        strings_["mig_adopting_note"] = "The node is restarting on your new wallet and will rescan the chain — this can take several minutes. Leave the wallet running; it reconnects automatically.";
         strings_["mig_working"] = "Creating your new seed wallet in an isolated node — this can take a minute. Your main wallet keeps running.";
         strings_["mig_seed_warning"] = "Write these 24 words down in order and store them offline. They are the only backup of your new wallet — if you lose them, the funds you migrate are gone forever.";
         strings_["mig_receive_addr"] = "New wallet receive address:";
@@ -521,6 +537,11 @@ void I18n::loadBuiltinEnglish()
         strings_["confirm_reinstall_daemon_title"] = "Install Bundled Daemon";
         strings_["confirm_reinstall_daemon_msg"] = "This stops the daemon, overwrites the installed dragonxd (and dragonx-cli/dragonx-tx) with the versions bundled in this wallet build, then restarts the node. Use this to recover or update the node binary.";
         strings_["confirm_reinstall_daemon_safe"] = "Your wallet, keys and blockchain data are not touched — only the daemon program files are replaced.";
+        strings_["daemon_update_title"] = "Update the node daemon?";
+        strings_["daemon_update_body"] = "This wallet build bundles a newer DragonX node than the one currently installed. Updating replaces the installed dragonxd (and dragonx-cli/dragonx-tx), then stops and restarts the node so the new version takes effect. Recommended — a newer node can add features (e.g. seed-phrase support) the old one lacks.";
+        strings_["daemon_update_safe"] = "Your wallet, keys and blockchain data are not touched — only the daemon program files are replaced. If you deliberately run a custom node, choose Keep current.";
+        strings_["daemon_update_now"] = "Update now";
+        strings_["daemon_update_keep"] = "Keep current";
         strings_["confirm_restart_daemon_title"] = "Restart Daemon";
         strings_["confirm_restart_daemon_msg"] = "This stops and restarts the daemon to apply the changed options. The wallet will briefly disconnect and reconnect.";
         strings_["lite_maintenance"] = "Maintenance";