ALBANY — When Amy Chin began digging for traces of her family history, the only clue she had was an old ship manifest showing her grandfather’s arrival to the U.S. in 1911 — well into the era of the Chinese Exclusion Act, which barred the immigration of all Chinese laborers for six decades. A lifelong resident of New York City, she didn’t expect the trail to lead north, to the far-flung reaches of New York that border Canada.