DOCS - BUG FIX - Backtick the chi_tor unit label so Documenter stops parsing it as a link

The clarified chi_tor docstrings wrote "diffusivity [m²/s] (a viscosity ...)",
which CommonMark reads as the link [m²/s](a viscosity ...). Documenter then fails
the InnerLayer autodocs page with :cross_references, invalid local link/image.
Backticking the unit is the convention CLAUDE.md prescribes for exactly this trap.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: d-burg

src/InnerLayer/SLAYER/LayerInputs.jl

@@ -91,7 +91,7 @@ profiles, without an intermediate file round-trip.
   - `chi_perp`  -- perpendicular heat diffusivity [m²/s]. Scalar or a
     callable of `psi` (default `1.0`).
   - `chi_tor`   -- Fitzpatrick's χ_φ: anomalous perpendicular ion MOMENTUM
-    diffusivity [m²/s] (a viscosity entering the vorticity and parallel-flow
+    diffusivity `[m²/s]` (a viscosity entering the vorticity and parallel-flow
     equations — not a heat diffusivity). Scalar or a callable of `psi`
     (default `1.0`).
   - `dr_val`    -- resistive interchange index `D_R = E + F + H²`

src/InnerLayer/SLAYER/LayerParameters.jl

@@ -199,7 +199,7 @@ parametrization (P_perp/P_tor/D_norm; the older magnetic/electron Prandtl
   - `zeff`    -- effective charge
   - `chi_perp` -- perpendicular energy diffusivity χ⊥ [m²/s]
   - `chi_tor`  -- Fitzpatrick's χ_φ, the anomalous perpendicular ion momentum
-    diffusivity [m²/s] (a viscosity, not heat; TJ Layer.tex eqs. — enters the
+    diffusivity `[m²/s]` (a viscosity, not heat; TJ Layer.tex eqs. — enters the
     vorticity and parallel-flow equations, τ_φ = r_s²/χ_φ)
   - `m`, `n`  -- poloidal / toroidal mode numbers at the surface
   - `dr_val`, `dgeo_val` -- inputs for the critical-Δ formula