feat(scanning): add library scanner with rules engine

- Add ScanRule model with configurable conditions
- Add FileAnalyzer for ffprobe-based media analysis
- Add LibraryScanner with manual, scheduled and watcher modes
- Add LanguageDetector for audio language detection
- Support rule-based filtering with priority evaluation

backend/scanning/detected_languages.py

@@ -0,0 +1,41 @@
+"""Model for storing detected audio languages."""
+from sqlalchemy import Column, Integer, String, DateTime, Index
+from sqlalchemy.sql import func
+
+from backend.core.database import Base
+
+
+class DetectedLanguage(Base):
+    """
+    Stores detected audio languages for files where metadata is undefined.
+
+    This cache prevents re-detecting the same file multiple times.
+    """
+
+    __tablename__ = "detected_languages"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    file_path = Column(String(1024), nullable=False, unique=True, index=True)
+    detected_language = Column(String(10), nullable=False)  # ISO 639-1 code
+    detection_confidence = Column(Integer, nullable=True)  # 0-100
+    detected_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+
+    # Indexes for performance
+    __table_args__ = (
+        Index('idx_detected_lang_path', 'file_path'),
+        Index('idx_detected_lang_language', 'detected_language'),
+    )
+
+    def __repr__(self):
+        return f"<DetectedLanguage {self.file_path}: {self.detected_language}>"
+
+    def to_dict(self) -> dict:
+        """Convert to dictionary."""
+        return {
+            "id": self.id,
+            "file_path": self.file_path,
+            "detected_language": self.detected_language,
+            "detection_confidence": self.detection_confidence,
+            "detected_at": self.detected_at.isoformat() if self.detected_at else None,
+        }
+