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/gun_harness/selector.nim

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+## Gun selector — picks best gun×power, computes aim angle, gates firing.
+## Fires highest power with acceptable hit rate when gun is aimed within
+## threshold and gunHeat == 0.
+
+import std/math
+import gun_interface
+import virtual_bullets
+
+const AimThresholdDeg* = 2.0  ## max angle error to fire; ponytail: tune per bot
+
+proc aimAngle*(selfX, selfY, targetX, targetY: float): float =
+  ## Absolute bearing in degrees (0=East, CCW+) toward (targetX, targetY).
+  result = radToDeg(arctan2(targetY - selfY, targetX - selfX))
+
+proc shouldFire*(currentGunDir, targetAngle, gunHeat: float): bool =
+  ## Returns true when gun is close enough and cool enough to fire.
+  var delta = (targetAngle - currentGunDir) mod 360.0
+  if delta > 180.0:  delta -= 360.0
+  elif delta < -180.0: delta += 360.0
+  abs(delta) <= AimThresholdDeg and gunHeat <= 0.0
+
+proc selectShot*(t: VirtualTracker): (GunId, int, float) =
+  ## Returns (gunId, powerBinIdx, power) — the shot to take this tick.
+  let gunId = t.bestGun()
+  let (binIdx, power) = t.bestPower(gunId)
+  result = (gunId, binIdx, power)