The Patriots reached an agreement with former Buffalo Bills fullback Reggie Gilliam on the opening day of the legal tampering period. The deal is reportedly a three-year contract worth up to $12 million, including $6 million in total guarantees and a $4.4 million payout in the first year. By signing Gilliam, the Patriots are not only poaching a key divisional rival’s asset but also doubling down on the physical, run-heavy…