feat: manage system appearance defaults

src/govoplan_admin/backend/api/v1/schemas.py

@@ -51,6 +51,8 @@ class SystemSettingsItem(BaseModel):
     enabled_language_codes: list[str] = Field(default_factory=list)
     settings: dict[str, Any] = Field(default_factory=dict)
     navigation: NavigationPreferencesPayload | None = None
+    appearance_palette: Literal["default", "civic_blue", "forest", "plum"] = "default"
+    appearance_palette_locked: bool = False
 
 
 class SystemSettingsDeltaResponse(BaseModel):
@@ -75,6 +77,8 @@ class SystemSettingsUpdateRequest(BaseModel):
     available_languages: list[LanguagePackageItem] | None = None
     enabled_language_codes: list[str] | None = None
     navigation: NavigationPreferencesPayload | None = None
+    appearance_palette: Literal["default", "civic_blue", "forest", "plum"] | None = None
+    appearance_palette_locked: bool | None = None
     change_request_id: str | None = None