feat(wallets): fixed max-height list + manage scanned folders

Two wallets-modal changes:

- The wallet list now always renders at its max height (kMaxVisibleRows) instead
  of shrinking to the wallet count, so the modal is a consistent size whether you
  have one wallet or many — fewer rows leave empty space, more than 7 scroll.

- Add a "Scanned folders" manager: each user-added scan folder is listed with a
  control to stop scanning it (removeExtraFolder + save + re-scan so its wallets
  drop out). Paths front-elide to keep the identifying leaf visible, with a
  full-path tooltip. The card-height math reserves the manager's rows so nothing
  clips. Two new i18n keys (wallets_scanned_folders / wallets_remove_folder),
  translated across all 8 languages; CJK subset rebuilt.

Verified on the sweep at 1.0 and 1.5x DPI: max-height list on both the few- and
many-wallet surfaces, the folder manager renders and stays clear of the footer.

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

src/util/i18n.cpp

@@ -287,6 +287,8 @@ void I18n::loadBuiltinEnglish()
         strings_["wallets_never"] = "Never opened";
         strings_["wallets_external_tt"] = "Outside your data directory \xE2\x80\x94 Open links it in place (no copy).";
         strings_["wallets_scan_folder"] = "Scan another folder for wallets\xE2\x80\xA6";
+        strings_["wallets_scanned_folders"] = "Scanned folders:";
+        strings_["wallets_remove_folder"] = "Stop scanning this folder";
         strings_["wallets_folder_invalid"] = "That folder doesn't exist.";
         strings_["wallets_new_label"] = "Create a new wallet:";
         strings_["wallets_new_hint"] = "Name (e.g. savings)";