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/library.go

@@ -41,7 +41,7 @@ func registerLibraryRoutes(cfg *Config) {
 			"library_id": libraryID,
 		}
 		c.Set("scan_request", scanReq)
-		return h.ScanEbooks(c)
+		return h.ScanLibrary(c)
 	})
 	adminLibrary.GET("/:id/media-items", func(c echo.Context) error {
 		libraryID := c.Param("id")