Adapt the refix AGENTS.md to this project: build commands, module
layout, C++/Swift/C-bridge style rules, and commit guidelines. C++
headers use .hpp and C headers use .h; the PLAN.md port table is
updated to match.
Co-Authored-By: qwen (qwen/qwen3.8-27b@q2_k_xl): wrote coding conventions
portersky