Fix: Improve author name extraction from Audiobookshelf API

Fixed issue where author names were showing as "Unknown" due to inconsistent
field names in the Audiobookshelf API response.

Changes:
- Added `extract_author_name()` helper function that tries multiple fields:
  1. `metadata.authorName` (string field)
  2. `metadata.authors` array (extracts first author's name)
  3. Falls back to "Unknown" only if neither exists
- Updated book sync logic to use the new robust extraction method
- Handles both dict and string formats in authors array

This resolves the issue where different Audiobookshelf instances or versions
may use different field structures for author metadata.

Fixes issue #6

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

app/main.py

@@ -29,6 +29,35 @@ from app.auth import (
 from app.services.stats import ReadingStatsService
 
 
+def extract_author_name(metadata: dict) -> str:
+    """
+    Extract author name from Audiobookshelf metadata.
+
+    Tries multiple fields in order:
+    1. authorName (string field)
+    2. authors array (extract first author's name)
+    3. Falls back to "Unknown"
+    """
+    # Try authorName field first
+    author_name = metadata.get("authorName")
+    if author_name:
+        return author_name
+
+    # Try authors array
+    authors = metadata.get("authors", [])
+    if authors and len(authors) > 0:
+        # Authors can be objects with 'name' field or just strings
+        first_author = authors[0]
+        if isinstance(first_author, dict):
+            author_name = first_author.get("name")
+            if author_name:
+                return author_name
+        elif isinstance(first_author, str):
+            return first_author
+
+    return "Unknown"
+
+
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     """Initialize database on startup."""
@@ -324,7 +353,7 @@ async def sync_with_audiobookshelf(
                 book = Book(
                     id=book_id,
                     title=metadata.get("title", "Unknown"),
-                    author=metadata.get("authorName", "Unknown"),
+                    author=extract_author_name(metadata),
                     narrator=metadata.get("narratorName"),
                     description=metadata.get("description"),
                     genres=json.dumps(metadata.get("genres", [])),
@@ -336,7 +365,7 @@ async def sync_with_audiobookshelf(
             else:
                 # Update existing book
                 book.title = metadata.get("title", book.title)
-                book.author = metadata.get("authorName", book.author)
+                book.author = extract_author_name(metadata)
                 if local_cover_url:  # Only update if download succeeded
                     book.cover_url = local_cover_url
                 book.updated_at = datetime.now()