Refactor helper drift in lib: centralize theme/translation and remove app() hotspots

lib/Service/Settings/SettingsAppGateway.php

@@ -57,7 +57,7 @@ class SettingsAppGateway
     {
         $value = $this->settingsMetadataGateway->getValue(SettingKeys::APP_THEME_KEY);
         $value = $value !== null ? strtolower(trim($value)) : '';
-        if (!in_array($value, $this->allowedThemes(), true)) {
+        if (!$this->isAllowedTheme($value)) {
             return null;
         }
 
@@ -67,7 +67,7 @@ class SettingsAppGateway
     public function setAppTheme(?string $theme, ?string $description = null): bool
     {
         $value = $theme !== null ? strtolower(trim($theme)) : '';
-        if ($value === '' || !in_array($value, $this->allowedThemes(), true)) {
+        if ($value === '' || !$this->isAllowedTheme($value)) {
             $value = null;
         }
 
@@ -75,6 +75,50 @@ class SettingsAppGateway
         return $this->settingsMetadataGateway->set(SettingKeys::APP_THEME_KEY, $value, $desc);
     }
 
+    /**
+     * @return array<string, string>
+     */
+    public function listThemes(): array
+    {
+        return $this->themeConfigService->all();
+    }
+
+    public function isAllowedTheme(?string $theme): bool
+    {
+        $value = strtolower(trim((string) $theme));
+        return $value !== '' && in_array($value, $this->allowedThemes(), true);
+    }
+
+    public function resolveDefaultTheme(): string
+    {
+        $settingTheme = $this->getAppTheme();
+        if ($settingTheme !== null) {
+            return $settingTheme;
+        }
+
+        $envTheme = strtolower(trim((string) (getenv('APP_THEME') ?: '')));
+        if ($this->isAllowedTheme($envTheme)) {
+            return $envTheme;
+        }
+
+        $allowedThemes = $this->allowedThemes();
+        if (in_array('light', $allowedThemes, true)) {
+            return 'light';
+        }
+
+        return (string) ($allowedThemes[0] ?? 'light');
+    }
+
+    public function normalizeTheme(?string $theme): string
+    {
+        $value = strtolower(trim((string) $theme));
+        if ($this->isAllowedTheme($value)) {
+            return $value;
+        }
+
+        return $this->resolveDefaultTheme();
+    }
+
     public function isUserThemeAllowed(): bool
     {
         $value = $this->settingsMetadataGateway->getValue(SettingKeys::APP_THEME_USER_KEY);
@@ -146,7 +190,7 @@ class SettingsAppGateway
 
     private function allowedThemes(): array
     {
-        return array_keys($this->themeConfigService->all());
+        return array_keys($this->listThemes());
     }
 
     public function normalizeLocale(?string $locale): string