Lithium Depletion Boundary in Brown Dwarfs (2D)

This 2D counterpart replaces the population view with a single-object, first-principles integration: pick a substellar mass, and the engine computes its core temperature from a Kelvin–Helmholtz contraction law, then integrates a real Arrhenius-style lithium-burn ODE forward in age to track exactly how much primordial lithium-7 survives. Sweeping the mass slider and re-running the same integration for ~70 masses traces the mass-vs-depletion-age boundary curve, which diverges toward "never" below a critical mass computed directly from the ignition-temperature parameter — reproducing the real observed lithium depletion boundary near 0.065 solar masses without it being hard-coded anywhere.