feat(ModularBot): pluggable bot with 4 guns, phantom meteor movement, radar harness

- Gun harness: virtual bullet tracker, rolling fitness, auto-selector
- Guns: head-on, linear (extrapolation), circular (integrated formula), tsetlin machine (learning)
- Movement: phantom meteor gravity engine (danger histograms, phantom bullets, fire detection)
- Radar: harness + radar_lock adapter
- Color-coded modules: turret/bullet color per gun, body per movement, scan per radar
- Beats Target, SpinBot, Crazy, TrackFire in 10-round battles

common_libs/guns/head_on.nim

@@ -0,0 +1,13 @@
+## Head-on gun: predict enemy stays at current position.
+## Simplest possible Gun implementation — baseline reference.
+
+import gun_harness/gun_interface
+
+type HeadOnGun* = object
+  discard
+
+proc predict*(g: var HeadOnGun, state: WorldState, bulletSpeed: float): GunPrediction =
+  GunPrediction(x: state.enemyX, y: state.enemyY)
+
+proc onResult*(g: var HeadOnGun, e: FeedbackEvent) =
+  discard  # analytical gun — no learning