chore: add agent files (#6082)

* chore: add agent files

Assisted-by: ClaudeCode:claude-opus-4.8
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* fix: better AGENTS.md

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* Apply suggestions from code review

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgkio@gmail.com>
Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>

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Signed-off-by: Henry Schreiner <henryfs@princeton.edu>
Co-authored-by: Ralf W. Grosse-Kunstleve <rwgkio@gmail.com>