feat(frontend): add OCR UI components and translations

- ScriptTypeSelect: native select for TYPEWRITER/HANDWRITING_LATIN/KURRENT
- OcrTrigger: wraps script type select + start button + confirmation dialog
- OcrProgress: SSE-based progress display with page counter and progress bar
- Paraglide translations for OCR (de/en/es): script types, trigger labels,
  confirmation dialog, progress messages, error messages
- ErrorCode type + getErrorMessage: OCR_SERVICE_UNAVAILABLE, OCR_JOB_NOT_FOUND,
  OCR_DOCUMENT_NOT_UPLOADED, OCR_PROCESSING_FAILED

All 687 frontend tests pass.

Refs #226

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/messages/en.json

@@ -500,5 +500,25 @@
 	"person_alias_delete_title": "Remove alias?",
 	"person_alias_delete_body": "This name will be removed from search results.",
 	"person_alias_btn_delete": "Remove",
-	"error_alias_not_found": "The name alias was not found."
+	"error_alias_not_found": "The name alias was not found.",
+	"error_ocr_service_unavailable": "The OCR service is not available.",
+	"error_ocr_job_not_found": "The OCR job was not found.",
+	"error_ocr_document_not_uploaded": "The document has no file — OCR is not possible.",
+	"error_ocr_processing_failed": "OCR processing failed.",
+	"ocr_script_type_typewriter": "Typewriter",
+	"ocr_script_type_handwriting_latin": "Handwriting (Latin)",
+	"ocr_script_type_handwriting_kurrent": "Handwriting (Kurrent/Sütterlin)",
+	"ocr_trigger_label": "Script type",
+	"ocr_trigger_select_placeholder": "Select script type…",
+	"ocr_trigger_btn": "Start OCR",
+	"ocr_trigger_btn_disabled": "Please select a script type",
+	"ocr_confirm_title": "Replace existing transcription?",
+	"ocr_confirm_body": "All {count} existing blocks will be deleted and replaced with OCR results. This action cannot be undone.",
+	"ocr_confirm_btn": "Replace",
+	"ocr_progress_heading": "OCR running",
+	"ocr_progress_page": "Page {current} of {total}",
+	"ocr_error_heading": "OCR failed",
+	"ocr_error_retry": "Try again",
+	"ocr_batch_running": "OCR running · {processed} of {total} documents complete",
+	"ocr_batch_done": "OCR complete · {processed} successful · {errors} failed"
 }