feat: implement logarithmic radius scaling for body sizes

- Changed scale_radius() from linear to logarithmic: scale * log10(radius)
- Adjusted size_scale from 1e-9 to 0.02 for better visual hierarchy
- Lowered min_radius from 0.5f to 0.01f for fine-grained visibility
- Updated rendering documentation with new scaling values

This handles extreme radius ranges (1.5M to 700M meters) while maintaining
visible size differences between Sun, planets, and moons.

docs/rendering.md

@@ -47,19 +47,22 @@ Vector3 sim_to_render(Vec3 pos, double scale) {
 - Optimized for solar system scale
 - Used for position transformations
 
-**Size Scale:** `1e-9` (same as distance scale)
-- Applied to body radii
-- Minimum visible radius: 0.5 units (ensures tiny bodies are visible)
+**Size Scale:** `0.02` (logarithmic radius scaling factor)
+- Applied to body radii using logarithmic scaling
+- Minimum visible radius: 0.01 units (ensures tiny bodies are visible)
 
 **Radius Scaling:**
 ```cpp
 float scale_radius(double radius, double scale) {
-    float scaled = (float)(radius * scale);
-    float min_radius = 0.5f;
+    float scaled = (float)(scale * log10(radius));
+    float min_radius = 0.01f;
     return (scaled > min_radius) ? scaled : min_radius;
 }
 ```
 
+Uses logarithmic scaling to handle extreme radius ranges (1.5M to 700M meters).
+Scale factor 0.02 produces: Sun ~0.18, planets 0.13-0.16, moons 0.12-0.13 render units.
+
 ## Camera System
 
 ### Camera Setup

src/renderer.cpp

@@ -87,7 +87,7 @@ void setup_camera(RenderState* render_state) {
     render_state->camera.projection = CAMERA_PERSPECTIVE;
 
     render_state->distance_scale = 1e-9;
-    render_state->size_scale = 1e-9;
+    render_state->size_scale = 0.02f;
 
     render_state->texture_loaded = false;
     render_state->spacecraft_texture = (Texture2D){0, 0, 0, 0, 0};
@@ -248,8 +248,8 @@ Vector3 sim_to_render(Vec3 pos, double scale) {
 
 // Scale a radius for rendering (with minimum visible size)
 float scale_radius(double radius, double scale) {
-    float scaled = (float)(radius * scale);
-    float min_radius = 0.5f;  // Minimum visible radius
+    float scaled = (float)(scale * log10(radius));
+    float min_radius = 0.01f;  // Minimum visible radius
     return (scaled > min_radius) ? scaled : min_radius;
 }