refactor(i18n): centralize unknownError and unify pdfToText note keys

src/js/logic/digital-sign-pdf-page.ts

@@ -758,9 +758,7 @@ async function processSignature(): Promise<void> {
     hideLoader();
     console.error('Signing error:', error);
     const errorMessage =
-      error instanceof Error
-        ? error.message
-        : t('tools:digitalSignPdf.unknownError');
+      error instanceof Error ? error.message : t('common.unknownError');
 
     // Check if this is a CORS/network error from certificate chain fetching
     if (

src/js/logic/wasm-settings-page.ts

@@ -216,7 +216,7 @@ async function initializePage() {
     } catch (e: unknown) {
       hideLoader();
       const errorMessage =
-        e instanceof Error ? e.message : t('tools:wasmSettings.unknownError');
+        e instanceof Error ? e.message : t('common.unknownError');
       showAlert(
         t('tools:wasmSettings.errorTitle'),
         t('tools:wasmSettings.failedSave', { message: errorMessage })