Lower the star halo floor so the inner orbits stay legible

The floor that stopped the Sun disappearing reached past Venus and up to
Earth, covering the two orbits it most needed to leave alone.

Halved, from 3.5% of the framed radius to 2%. The halo's visual radius is
half its extent, so that puts its edge at 1% of the framed radius, and the
orbits it has to clear sit at their own fraction of the same radius: in
the solar system, framed to hold Pluto, Venus is at 1.3% and Earth at
1.8%. Both are now outside it, and the star still reads at about nine
pixels across on a typical window.

Mercury, at 0.7%, is still inside — and would be at any halo large enough
to see, since its orbit is only three pixels wide at that range. That is
now a pinned test rather than an oversight.

The floor was only ever the lower bound; the tests now state the upper one
too, in the terms the trade is actually made in — pixels on screen for
visibility, AU against real orbits for clearance.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaySiNst4HhDXBHnMy8p5G

README.md

@@ -56,7 +56,9 @@ system those differ by a factor of a hundred. At the distance that fits Pluto in
 that stays clear of Mercury is about a pixel across, and no radius satisfies both. So the disc
 stays honest to the orbits and the star's halo carries its visibility, floored against the framed
 radius: light is not a surface, and a glow reaching past the innermost orbit says the star is
-bright rather than that it is large.
+bright rather than that it is large. That floor is bounded from both sides — large enough that
+the star reads at a glance, small enough that Venus's and Earth's orbits stay legible as rings
+around it. Mercury's, three pixels wide at that range, does not survive either way.
 
 **Body detail** — a dedicated close-up scene and info panel for one planet, moon or exoplanet,
 with real photography where NASA/ESA/USGS imagery exists, and a surface derived from the body's