Add AGENTS.md guidance for non-conda execution environments (Apptainer, Docker, HPC modules)

[chaibhave]

Reason

AGENTS.md currently instructs agents to use the MOOSE conda environment (conda activate moose) as the only method for running ./tmap8-opt and run_tests. In practice, developers and CI systems also use alternative execution environments — Apptainer/Singularity containers, Docker images, and HPC environment modules — to run TMAP8 and other MOOSE-based applications. Without guidance for these environments, an AI agent working on an HPC cluster or inside a container will either fail to locate the executable or blindly attempt conda activation in an environment where it is not available.

Design

Add a short subsection (or bullet list) under the ## Environment section of AGENTS.md that covers:

• Apptainer / Singularity: how to invoke the app through apptainer exec <image> ./tmap8-opt -i <file>.i and run tests via apptainer exec <image> ./run_tests
• Docker: equivalent docker run invocation pattern
• HPC environment modules: that module load moose (or the site-specific module name) may replace conda activate moose on HPC systems, and how to check which is appropriate
• A note that if none of the above activations succeed the agent should stop and ask the user how to access the executable, rather than guessing

Impact

Documentation-only change to AGENTS.md. No API or code changes. Improves agent robustness on non-conda systems without affecting existing conda-based workflows.