DOC: Move equations to Notes in kinematics docstrings

[manduinca]

Description Of Changes

Scoped to metpy.calc.kinematics for a focused first pass at #2677. Moves the equation blocks and implementation details out of the function description (above Parameters) and into the Notes section, so they render below Parameters/Returns.

Affects frontogenesis, storm_relative_helicity, potential_vorticity_baroclinic, potential_vorticity_barotropic, inertial_advective_wind and q_vector. This leaves the module consistent with the pattern already used here by vorticity, divergence, advection and total_deformation.

potential_vorticity_barotropic and q_vector had no Notes section, so I added one and moved the stray .. versionchanged:: into it. Docstrings only — no code, signatures or behaviour changed, and the doctests are untouched. Happy to follow up with the remaining modules (thermo, indices, …) in separate PRs.

Checklist

• Closes Move equations to Notes #2677
• Tests added (docstring-only change)
• Fully documented

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