fix(ocr): ensure Tesseract language data for embed_text_layer regardless of active OCR provider

Root cause: ensure_ocr_languages_from_settings() only downloaded tessdata
when the 'tesseract' provider was active, but embed_text_layer() uses
ocrmypdf (which needs tessdata) as a fallback for ALL OCR providers.

- embed_text_layer(): call ensure_tesseract_languages(language) after
  confirming ocrmypdf is on PATH, so language data is present before
  ocrmypdf is invoked (prevents exit code 3 for fra/deu/etc.)
- ensure_ocr_languages_from_settings(): extend the condition from
  'tesseract' in active_providers to also trigger when ocrmypdf is
  on PATH, enabling proactive pre-download at startup for any config
- Tests: mock shutil.which and ensure_tesseract_languages in affected
  test cases; rename azure-only test and add new test for ocrmypdf case

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/utils/ocr_provider.py

@@ -93,6 +93,19 @@ def embed_text_layer(input_pdf_path: str, output_pdf_path: str, *, language: str
         )
         return False
 
+    # Ensure Tesseract language data is present before invoking ocrmypdf.
+    # ocrmypdf uses Tesseract internally regardless of which OCR provider is
+    # active, so we must guarantee the tessdata files exist here.
+    from app.utils.ocr_language_manager import ensure_tesseract_languages  # noqa: PLC0415
+
+    missing_langs = ensure_tesseract_languages(language)
+    if missing_langs:
+        logger.warning(
+            "[embed_text_layer] Missing Tesseract language data for: %s – "
+            "text-layer embedding may fail or produce degraded results.",
+            ", ".join(missing_langs),
+        )
+
     in_place = input_pdf_path == output_pdf_path
     if in_place:
         import tempfile