add an overview to fix configuration bugs

docs/config_assumptions.md

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+# Configuration File Assumptions and Issues
+
+## Key Assumptions Found:
+
+### **1. Format Assumptions (from config_loader.cpp)**
+- Line buffer limited to 256 characters (config_loader.cpp:30)
+- Name limited to 64 characters (config_loader.cpp:31)
+- All 10 fields must be present: `name mass radius x y z parent_index r g b` (config_loader.cpp:19)
+- File format is space-delimited
+
+### **2. Solar System Configuration Issues:**
+
+**Problem 1: Moon position is incorrect**
+- Earth is at: `(1.496e11, 0, 0)` m
+- Moon is at: `(1.500e11, 0, 0)` m
+- Distance: ~4 million km, but Earth-Moon distance should be ~384,400 km (~3.844e8 m)
+- The Moon should be at approximately `(1.496e11 + 3.844e8, 0, 0)` or similar
+
+**Problem 2: Jupiter's moons positions**
+- Jupiter is at: `(7.785e11, 0, 0)` m
+- Io is at: `(8.207e11, 0, 0)` m - **422 million km from Jupiter** (should be ~422,000 km = 4.22e8 m)
+- Europa is at: `(8.456e11, 0, 0)` m - **671 million km from Jupiter** (should be ~671,000 km = 6.71e8 m)
+- Ganymede/Callisto have similar issues
+
+The moon positions appear to use **absolute coordinates** matching their orbital radii around the Sun, not relative positions around their parent bodies!
+
+### **3. Binary Star Configuration Issues:**
+
+**Problem 1: Both stars have parent_index = -1**
+- StarA: `parent_index = -1`
+- StarB: `parent_index = -1`
+- This means both are treated as root bodies with zero velocity (config_loader.cpp:69)
+- They won't orbit each other!
+
+**Problem 2: Planet positions**
+- PlanetA1 is at `(3.5e11, 0, 0)` while StarA is at `(3.0e11, 0, 0)` - only 50 million km apart
+- PlanetB1 is at `(-4.2e11, 0, 0)` while StarB is at `(-3.7e11, 0, 0)` - only 50 million km apart
+- These seem reasonable as absolute positions, but the velocity calculation assumes circular orbits
+
+### **4. Velocity Calculation Assumptions (config_loader.cpp:63-118):**
+- All orbits are assumed to be **circular**
+- Orbits are calculated in the XY plane perpendicular to Z-axis (config_loader.cpp:92)
+- Root bodies (parent_index = -1) get zero velocity
+- Velocities are calculated relative to parent, then parent's velocity is added
+
+### **5. Critical Assumption:**
+The code assumes **positions are absolute (heliocentric)**, but for child bodies like moons, the **positions in the config should be relative to their parent**. This is not clearly documented and appears inconsistent!
+
+## Recommended Actions:
+
+1. Fix moon positions in solar_system.txt to be correct absolute coordinates
+2. Fix binary star system to have one star orbit the other (or implement barycenter)
+3. Document whether positions should be absolute or relative to parent
+4. Add validation to check if child body positions make sense relative to parent