fix(themes): stop the theme editor from failing without saying so

"Duplicate to edit" logged its failure and did nothing else — a button
that does nothing is indistinguishable from having clicked the wrong
thing. Worse, every colour edit runs through mutate_active_theme, which
returned early on a write failure: the picker moved, the theme did not,
and nothing said why.

Both now report, through the same notify_err the rest of the app uses.
On a themes folder the user cannot write, that reads "Could not
duplicate the theme: You do not have permission." rather than
"Permission denied (os error 13)", or nothing at all.

src/ui/app.rs

@@ -1388,7 +1388,17 @@ impl Tty7App {
                 crate::ui::presets::load_registry(cx);
                 self.set_preset(&new_id, window, cx);
             }
-            Err(e) => log::warn!("failed to duplicate theme: {e}"),
+            // A button that does nothing is the worst kind of failure: there
+            // is no way to tell it from "I clicked the wrong thing".
+            Err(e) => {
+                log::warn!("failed to duplicate theme: {e}");
+                crate::ui::host_ops::HostOps::notify_err(
+                    window,
+                    cx,
+                    t(L10nKey::ThemeDuplicateFailed),
+                    &e,
+                );
+            }
         }
     }
 
@@ -1405,7 +1415,10 @@ impl Tty7App {
         }
         mutate(&mut theme);
         if let Err(e) = crate::ui::presets::write_theme_file(&theme) {
+            // Every colour edit runs through here. Without this the picker
+            // moves, the theme does not, and nothing says why.
             log::warn!("failed to write theme file: {e}");
+            crate::ui::host_ops::HostOps::notify_err(window, cx, t(L10nKey::ThemeSaveFailed), &e);
             return;
         }
         crate::ui::presets::load_registry(cx);

src/ui/i18n/en.rs

@@ -134,6 +134,9 @@ pub fn translate_en(key: L10nKey) -> &'static str {
         }
         L10nKey::SettingsAnsiColors => "ANSI colors",
         L10nKey::SettingsCustomThemes => "Custom themes",
+        L10nKey::ThemeDuplicateFailed => "Could not duplicate the theme",
+        L10nKey::ThemeSaveFailed => "Could not save the theme",
+        L10nKey::OpenInFileManagerFailed => "Could not open {path}",
         L10nKey::SettingsCustomThemesIntro => {
             "Duplicate a theme to edit its colors here, or drop your own in the themes folder: a tty7 YAML theme or an iTerm2 .itermcolors scheme."
         }

src/ui/i18n/ja.rs

@@ -134,6 +134,9 @@ pub fn translate_ja(key: L10nKey) -> Option<&'static str> {
         L10nKey::SettingsBackgroundImageDesc => "背景色の上、テキストの下に表示されます",
         L10nKey::SettingsAnsiColors => "ANSI カラー",
         L10nKey::SettingsCustomThemes => "カスタムテーマ",
+        L10nKey::ThemeDuplicateFailed => "テーマを複製できませんでした",
+        L10nKey::ThemeSaveFailed => "テーマを保存できませんでした",
+        L10nKey::OpenInFileManagerFailed => "{path} を開けませんでした",
         L10nKey::SettingsCustomThemesIntro => {
             "テーマを複製して色を編集するか、テーマフォルダに自作テーマ（tty7 の YAML テーマまたは iTerm2 の .itermcolors スキーム）を置けます"
         }

src/ui/i18n/mod.rs

@@ -161,6 +161,9 @@ pub enum L10nKey {
     SettingsBackgroundImageDesc,
     SettingsAnsiColors,
     SettingsCustomThemes,
+    ThemeDuplicateFailed,
+    ThemeSaveFailed,
+    OpenInFileManagerFailed,
     SettingsCustomThemesIntro,
     SettingsDuplicateToEdit,
     SettingsHosts,
@@ -1202,6 +1205,9 @@ mod tests {
             L10nKey::SettingsBackgroundImageDesc,
             L10nKey::SettingsAnsiColors,
             L10nKey::SettingsCustomThemes,
+            L10nKey::ThemeDuplicateFailed,
+            L10nKey::ThemeSaveFailed,
+            L10nKey::OpenInFileManagerFailed,
             L10nKey::SettingsCustomThemesIntro,
             L10nKey::SettingsDuplicateToEdit,
             L10nKey::SettingsHosts,

src/ui/i18n/zh.rs

@@ -118,6 +118,9 @@ pub fn translate_zh(key: L10nKey) -> Option<&'static str> {
         L10nKey::SettingsBackgroundImageDesc => "叠加在背景色之上、文字之下。",
         L10nKey::SettingsAnsiColors => "ANSI 颜色",
         L10nKey::SettingsCustomThemes => "自定义主题",
+        L10nKey::ThemeDuplicateFailed => "无法复制主题",
+        L10nKey::ThemeSaveFailed => "无法保存主题",
+        L10nKey::OpenInFileManagerFailed => "无法打开 {path}",
         L10nKey::SettingsCustomThemesIntro => {
             "复制一个主题后可在此编辑其颜色，或者把自定义主题放入主题文件夹：tty7 YAML 主题或 iTerm2 的 .itermcolors 方案。"
         }