fix: ensure all NFO properties are written on creation

- Add showtitle and namedseason to mapper output
- Add multi-language fallback (en-US, ja-JP) for empty overview
- Use search result overview as last resort fallback
- Add tests for new NFO creation behavior

src/core/services/nfo_service.py

@@ -160,7 +160,7 @@ class NFOService:
             
             logger.info(f"Found match: {tv_show['name']} (ID: {tv_id})")
             
-            # Get detailed information
+            # Get detailed information with multi-language image support
             details = await self.tmdb_client.get_tv_show_details(
                 tv_id,
                 append_to_response="credits,external_ids,images"
@@ -169,8 +169,12 @@ class NFOService:
             # Get content ratings for FSK
             content_ratings = await self.tmdb_client.get_tv_show_content_ratings(tv_id)
             
-            # Enrich with English fallback for empty overview/tagline
-            details = await self._enrich_details_with_fallback(details)
+            # Enrich with fallback languages for empty overview/tagline
+            # Pass search result overview as last resort fallback
+            search_overview = tv_show.get("overview") or None
+            details = await self._enrich_details_with_fallback(
+                details, search_overview=search_overview
+            )
             
             # Convert TMDB data to TVShowNFO model
             nfo_model = tmdb_to_nfo_model(
@@ -267,9 +271,8 @@ class NFOService:
             # Get content ratings for FSK
             content_ratings = await self.tmdb_client.get_tv_show_content_ratings(tmdb_id)
             
-            # Enrich with English fallback for empty overview/tagline
-            details = await self._enrich_details_with_fallback(details)
-            
+            # Enrich with fallback languages for empty overview/tagline
+            details = await self._enrich_details_with_fallback(details)            
             # Convert TMDB data to TVShowNFO model
             nfo_model = tmdb_to_nfo_model(
                 details,
@@ -381,20 +384,26 @@ class NFOService:
     async def _enrich_details_with_fallback(
         self,
         details: Dict[str, Any],
+        search_overview: Optional[str] = None,
     ) -> Dict[str, Any]:
-        """Enrich TMDB details with English fallback for empty fields.
+        """Enrich TMDB details with fallback languages for empty fields.
 
         When requesting details in ``de-DE``, some anime have an empty
         ``overview`` (and potentially other translatable fields).  This
-        method detects empty values and fills them from the English
-        (``en-US``) endpoint so that NFO files always contain a ``plot``
-        regardless of whether the German translation exists.
+        method detects empty values and fills them from alternative
+        languages (``en-US``, then ``ja-JP``) so that NFO files always
+        contain a ``plot`` regardless of whether the German translation
+        exists.  As a last resort, the overview from the search result
+        is used.
 
         Args:
             details: TMDB TV show details (language ``de-DE``).
+            search_overview: Overview text from the TMDB search result,
+                used as a final fallback if all language-specific
+                requests fail or return empty overviews.
 
         Returns:
-            The *same* dict, mutated in-place with English fallbacks
+            The *same* dict, mutated in-place with fallback values
             where needed.
         """
         overview = details.get("overview") or ""
@@ -403,32 +412,46 @@ class NFOService:
             # Overview already populated – nothing to do.
             return details
 
-        logger.debug(
-            "German overview empty for TMDB ID %s, fetching English fallback",
-            details.get("id"),
-        )
+        tmdb_id = details.get("id")
+        fallback_languages = ["en-US", "ja-JP"]
 
-        try:
-            en_details = await self.tmdb_client.get_tv_show_details(
-                details["id"],
-                language="en-US",
+        for lang in fallback_languages:
+            if details.get("overview"):
+                break
+
+            logger.debug(
+                "Trying %s fallback for TMDB ID %s",
+                lang, tmdb_id,
             )
 
-            if en_details.get("overview"):
-                details["overview"] = en_details["overview"]
-                logger.info(
-                    "Used English overview fallback for TMDB ID %s",
-                    details.get("id"),
+            try:
+                lang_details = await self.tmdb_client.get_tv_show_details(
+                    tmdb_id,
+                    language=lang,
                 )
 
-            # Also fill tagline if missing
-            if not details.get("tagline") and en_details.get("tagline"):
-                details["tagline"] = en_details["tagline"]
-        except Exception as exc:  # pylint: disable=broad-except
-            logger.warning(
-                "Failed to fetch English fallback for TMDB ID %s: %s",
-                details.get("id"),
-                exc,
+                if not details.get("overview") and lang_details.get("overview"):
+                    details["overview"] = lang_details["overview"]
+                    logger.info(
+                        "Used %s overview fallback for TMDB ID %s",
+                        lang, tmdb_id,
+                    )
+
+                # Also fill tagline if missing
+                if not details.get("tagline") and lang_details.get("tagline"):
+                    details["tagline"] = lang_details["tagline"]
+            except Exception as exc:  # pylint: disable=broad-except
+                logger.warning(
+                    "Failed to fetch %s fallback for TMDB ID %s: %s",
+                    lang, tmdb_id, exc,
+                )
+
+        # Last resort: use search result overview
+        if not details.get("overview") and search_overview:
+            details["overview"] = search_overview
+            logger.info(
+                "Used search result overview fallback for TMDB ID %s",
+                tmdb_id,
             )
 
         return details