refactor(api): rename ScanEbooks to ScanLibrary for clarity

- Rename ScanEbooks method to ScanLibrary to reflect generic media scanning

- Rename ScanEbooksRequest to ScanLibraryRequest

- Update route handlers in scanner.go and library.go

- Rename scan_ebooks.md to scan_library.md

- No breaking changes: API endpoint remains POST /api/scanner/scan

internal/router/scanner.go

@@ -8,7 +8,7 @@ import (
 // registerScannerRoutes registers all scanner-related endpoints
 func registerScannerRoutes(admin *echo.Group, h *handlers.Handler) {
 	// Scanner routes (admin only)
-	admin.POST("/scanner/scan", h.ScanEbooks)
+	admin.POST("/scanner/scan", h.ScanLibrary)
 	admin.POST("/scanner/start", h.StartScanner)
 	admin.POST("/scanner/stop", h.StopScanner)
 	admin.GET("/scanner/status/:jobId", h.GetScanStatus)