[antonio-leblanc]

Adds \ ests/mnh_coupled.bash\ and updates \docs/mnh/coupledMNHInstall.md\ to start from it:

• Checks prerequisites (printing the \�pt install\ line without running \sudo), downloads Meso-NH 6.0.1 from Zenodo (checking MD5), builds Meso-NH and ForeFire with MPI, links \libForeFire.so, and runs \ ests/mnh_real_nested.
• --compare \ builds both trees, runs the case four times (\ his-1, \other-1, \ his-2, \other-2) and compares all outputs byte for byte, separating known run-to-run noise (\RUN12..FIRE..nc\ timestamps and \MODEL*/output.*.air_density) from real differences.

Ref #266

[antonio-leblanc]