Fix license metadata to BSD-3-Clause

[neuromechanist]

The LICENSE file is BSD 3-Clause, but pyproject.toml, version.py, and README.md declared MIT. This corrects the metadata to match the actual license (BSD 3-Clause), which matters for JOSS submission (license clarity).

Changes

• pyproject.toml: license = {text = "BSD-3-Clause"}; classifier License :: OSI Approved :: BSD License.
• pyAMICA/version.py: LICENSE = "BSD-3-Clause"; classifier updated to BSD.
• README.md: license section now says BSD 3-Clause and links LICENSE.

No code changes. The LICENSE file itself (already BSD 3-Clause) is unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.44%. Comparing base (e5c58ee) to head (849afd0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #98   +/-   ##
=======================================
  Coverage   79.44%   79.44%           
=======================================
  Files          14       14           
  Lines        1975     1975           
  Branches      337      337           
=======================================
  Hits         1569     1569           
  Misses        301      301           
  Partials      105      105           

Files with missing lines	Coverage Δ
pyAMICA/version.py	90.62% <100.00%> (ø)

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