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/linear.nim

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+## Linear gun: predict enemy continues at current velocity and heading.
+## Coordinate system: 0° = East, CCW positive (Tank Royale standard).
+
+import std/math
+import gun_harness/gun_interface
+
+type LinearGun* = object
+  discard
+
+proc predict*(g: var LinearGun, state: WorldState, bulletSpeed: float): GunPrediction =
+  let dist = hypot(state.enemyX - state.selfX, state.enemyY - state.selfY)
+  let ticksToArrive = dist / bulletSpeed
+  let headingRad = degToRad(state.enemyHeading)
+  var px = state.enemyX + cos(headingRad) * state.enemySpeed * ticksToArrive
+  var py = state.enemyY + sin(headingRad) * state.enemySpeed * ticksToArrive
+  # Clamp to arena bounds
+  px = clamp(px, 0.0, state.arenaWidth)
+  py = clamp(py, 0.0, state.arenaHeight)
+  GunPrediction(x: px, y: py)
+
+proc onResult*(g: var LinearGun, e: FeedbackEvent) =
+  discard  # analytical gun — no learning