[mmshad]

Adds a partition setting and steps to run the GPU jobs of the example on kempner_interactive.

• Adds round.partition next to round.constraint. The loops pass both to every round job they submit.
• Before a search starts, the loop job checks the round job scripts with sbatch --test-only. If SLURM would reject them, the loop stops before any agent step.
• An array job no longer counts a wait behind its own running tasks against the queue limit, so the rounds of a wave can run in turns with wave.max_parallel: 1. The loop plans the time of a wave for the turns.
• When a job reaches the queue limit, the loop log shows the SLURM reason, for example QOSMaxGRESPerUser.
• The README has a new section, Run on kempner_interactive. AGENTS.md and the experiment files show the new settings.
• Tested on kempner_interactive: the baseline, round 1, and a small run of each loop. 119 unit tests pass.
• Add kempner_interactive steps to the agentic workflow examples kempner-computing-handbook#457 adds the same steps to the two example chapters. Merge this PR first.

Closes #3