feat(market): explain why the portfolio Save button is disabled

Hovering the disabled Save button now shows which requirement is missing
(name / at least one address / a manual price above 0), mirroring the
send-tab disabled-submit tooltip idiom (IsItemHovered(AllowWhenDisabled)).
The hint only appears for a validation gap — not the self-evident "nothing
changed" case.

Adds portfolio_save_need_{name,address,price} to the English source and all
eight translations; rebuilds the CJK subset font for the new JA/KO/ZH glyphs.

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

src/util/i18n.cpp

@@ -1405,6 +1405,9 @@ void I18n::loadBuiltinEnglish()
         strings_["portfolio_cancel"] = "Cancel";
         strings_["portfolio_revert"] = "Revert";
         strings_["portfolio_close"] = "Close";
+        strings_["portfolio_save_need_name"] = "Enter a name to save this group.";
+        strings_["portfolio_save_need_address"] = "Add at least one address to save.";
+        strings_["portfolio_save_need_price"] = "Enter a manual price above 0 to save.";
         strings_["portfolio_untitled"] = "Untitled";
         strings_["portfolio_detail_empty"] = "Select a group on the left, or add one, to edit it.";
         strings_["portfolio_add_to"] = "Add to portfolio";