feat(diagnostics): add "Copy diagnostics" + "Open log folder" actions (Foundation QoL)

Settings (logging section) gains two support-friendly actions, now that the logging
foundation actually produces logs (W7-2):

- Open log folder: opens the config dir (Platform::openFolder) so users can find
  dragonx-debug.log / dragonx-crash.log.

- Copy diagnostics: copies a plaintext support snapshot to the clipboard via the new
  App::buildDiagnosticsReport() — version, build variant, platform, connection status,
  active wallet path + existence + size, encryption/lock state, sync heights, and (full-
  node) daemon status/running/crash-count/lastError, plus the log paths. No secrets.

Build-clean; ctest 1/1. Remaining QoL: persistent alert history, a daemon/RPC error
banner, and the W6-2 refresh-staleness badge. See docs/wallet-hardening.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -1322,6 +1322,11 @@ void I18n::loadBuiltinEnglish()
         strings_["loading_stall_body"] = "The daemon has been initializing for %.0fs. This can be normal after an update or on first launch (loading the block index or rescanning) — it will connect automatically once ready.";
         strings_["loading_stall_hint"] = "Still stuck? Open Settings and use Restart Daemon, or check the Console for details.";
         strings_["sb_plaintext_remote_blocked"] = "Refusing to send RPC credentials over plaintext to a remote host. Add rpcallowplaintext=1 to DRAGONX.conf to allow it, or enable TLS with rpctls=1.";
+        strings_["settings_open_log_folder"] = "Open log folder";
+        strings_["settings_copy_diagnostics"] = "Copy diagnostics";
+        strings_["settings_diagnostics_copied"] = "Diagnostics copied to clipboard";
+        strings_["tt_open_log_folder"] = "Open the folder containing the debug and crash logs";
+        strings_["tt_copy_diagnostics"] = "Copy a support snapshot (version, daemon/wallet/log state — no secrets) to the clipboard";
         strings_["sb_dragonxd_running"] = "dragonxd running";
         strings_["sb_dragonxd_stopping"] = "Stopping dragonxd...";
         strings_["sb_dragonxd_stopped"] = "dragonxd stopped";