chore: add Codex project context and agent guidance

.agents/skills/kst4contest-change/references/roadmap.md

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+# Deferred and roadmap context
+
+This file is background only. Do not implement these items merely because they are mentioned here.
+
+## Propagation model
+
+After the manual audit, Marc intends to revisit and improve KST4Contest propagation modelling.
+
+Exploration areas include:
+
+- higher-density Copernicus GLO-30 terrain sampling;
+- Fresnel-zone analysis;
+- diffraction modelling;
+- simplified ray tracing / multi-segment paths;
+- VHF/UHF/microwave contest applicability, including around 1296 MHz and above;
+- practical contest-oriented prediction rather than academic complexity for its own sake.
+
+This requires a fresh concept before implementation.
+
+## Rule
+
+Roadmap context must never silently enlarge the scope of a current task.