docs: minor documentation improvements

Author: mpusz

docs/reference/cheat_sheet.md

@@ -374,7 +374,7 @@ double speed_value = (100 * km / h).force_numerical_value_in(m / s); // 27 (2)
     // quantity<si::metre, int> invalid = 1.5 * m;            // ✗ Error: double → int needs explicit cast
     ```
 
-=== "Affine Space Safety"
+=== "Mathematical Space Safety"
 
     Distinguishes absolute points from relative differences (vectors):
 

docs/tutorials/quick_start/simple_math.md

@@ -90,7 +90,7 @@ quantity result = 1 * km + 2000 * m;  // Result: 3000 m
 
 Try these in the editor above:
 
-1. **Calculate fuel efficiency**: `quantity fuel = 50 * l;` then `total_distance / fuel` (km/L)
+1. **Calculate fuel efficiency**: `quantity fuel = 50 * L;` then `total_distance / fuel` (km/L)
 2. **Multiple operations**: Try `(trip1 + trip2) / (time * 2)`
 3. **Acceleration**: `quantity velocity = 30 * m / s; quantity duration = 5 * s;` then
   `velocity / duration`