Simple Gravity II: Field Equation and Spherical Solution

This work introduces the nonlinear scalar field equation underlying the Simple Gravity framework: ∇²Φ = 4πGρ + (1/c²)(∇Φ)². An exact spherically symmetric solution is derived, recovering the Newtonian limit at large distances while incorporating nonlinear corrections near massive bodies. This establishes the field-theoretic foundation of the theory. This is the second paper in the Simple Gravity series.