cuopt-agent: add duals-interpretation guidance to the debugging skill

[cafzal]

What

Adds resources/interpreting_duals.md to the cuopt-agent's cuopt-debugging skill: guidance for turning a solved LP/QP's DualValue / ReducedCost / Slack into a decision read — which constraint is the binding bottleneck and what relaxing it is worth (its dual value), and which unused option is closest to entering (reduced cost). Linked from the skill's SKILL.md.

Why

The skill already shows how to read duals (diagnostic_snippets.md) but not what they mean for the decision. It also makes the scope explicit — consistent with the main-repo dual/sensitivity work (NVIDIA/cuopt#1393, #1406): duals exist for continuous (LP/QP) solves off linear constraints. Two cases return none — an integer model (the max-supply model is a MILP) and a quadratic constraint (a quadratic objective is fine) — with the difference-adjacent-solves / LP-relaxation fallback called out for the MILP.

Notes

• Pure guidance — a skill resources/ markdown plus a one-line SKILL.md pointer; no code or model changes.
• Grounded in the max-supply shape (resource-hour caps and per-period supply limits as the binding bottlenecks).

Companion to the dual / sensitivity work in #154 (LP duals in the diet example) and #157 (the agent's multi-objective scenario).

[cafzal]

@rgsl888prabhu small one: adds duals-interpretation guidance (decision read of DualValue/ReducedCost) to the agent's debugging skill. Ready for review.