Charlotte City Council voted unanimously Monday to approve the city’s biggest new development in at least two decades, setting the stage to bring millions of square feet of new office space, thousands of homes and hundreds of shops and restaurants to a quiet corner of the county. In total, the developers estimate the River District will generate more than $3 billion worth of new, taxable property in the city. The city’s capital investment program currently calls for spending $44.7 million worth of bond money to improve roads in the area. City staff will fine-tune the agreement with the developers and bring it to City Council next spring.