feat(wallet): detect a corrupt target wallet on switch + offer -salvagewallet repair

When a switch fails, the failure modal now distinguishes a CORRUPT target wallet
from other failures and offers a one-click repair:
- The switch worker watermarks the node's captured console output before the
  start and, if the node dies in init, scans this start's output for a corruption
  signature ("Failed to rename … .bak" / "salvage failed" / "wallet.dat corrupt" /
  "Error loading wallet") → sets switch_wallet_corrupt_.
- The Failed modal then shows an accurate "this wallet appears corrupt" message
  (instead of the generic "Couldn't open that wallet") plus a "Try to repair
  (salvage)" button that retries the switch with the target node started under
  -salvagewallet (recovers readable keypairs; implies -rescan).
- EmbeddedDaemon::setSalvageOnNextStart (one-shot, precedence salvage > zap >
  rescan) + controller forwarder; switchToWallet gains a salvage arg.

Salvage operates only on the corrupt target (never the good wallet, no fund
movement). Adversarially verified: output isolation, one-shot lifecycle, state
handling, re-entrancy, no success-path regression.

i18n (EN + 8 languages) + 2 new CJK glyphs baked into the subset font.

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

src/util/i18n.cpp

@@ -1057,6 +1057,8 @@ void I18n::loadBuiltinEnglish()
         strings_["switch_progress_elapsed"] = "Elapsed";
         strings_["switch_progress_default_wallet"] = "Default wallet";
         strings_["switch_progress_external_wallet"] = "External wallet";
+        strings_["switch_corrupt_body"] = "This wallet appears corrupt — the node couldn't open it. Restore it from a backup, re-create it, or try to repair it.";
+        strings_["switch_corrupt_repair"] = "Try to repair (salvage)";
 
         // Receive Tab
         strings_["receiving_addresses"] = "Your Receiving Addresses";