feat: bigger characters (16 sub-bodies), wider terminal viewport

- Entity: 16 sub-bodies (was 7), radius 0.7 (was 0.4), full humanoid
  shape: head, shoulders, torso, arms, hips, legs, feet
- Terminal: viewport up to 250x80 (was 120x50), uses full terminal size
- Camera: uses renderer viewport dimensions instead of hardcoded values
- Physics: constraint correction clamped to 0.5 cells max, 8 substeps
  (was 4), gravity 0.04 (was 0.08), collision pass after each constraint
  iteration to prevent tunneling with larger bodies
- Player: move_speed 0.3, jump_force 1.2 for bigger body
- Spawn: 6 cells above surface (was 4) for taller body

tests/integration.rs

@@ -87,7 +87,7 @@ fn pipe_protocol_init_and_step() {
     let mut output = String::new();
     let stdout = child.stdout.as_mut().expect("failed to open stdout");
     use std::io::Read;
-    let mut buf = [0u8; 4096];
+    let mut buf = [0u8; 65536];
     let n = stdout.read(&mut buf).expect("read");
     output.push_str(&String::from_utf8_lossy(&buf[..n]));