feat(ModularBot): melee targeting — multi-enemy tracker, per-enemy gun fitness, radar auto-switch

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

common_libs/targeting/enemy_tracker.nim

@@ -0,0 +1,54 @@
+## Per-enemy state table. Keyed by bot ID.
+## Tank Royale: 0° = East.
+
+import std/tables
+import std/math
+
+type
+  EnemyState* = object
+    id*:          int
+    x*, y*:       float
+    heading*:     float  ## degrees
+    speed*:       float
+    energy*:      float
+    lastSeenTick*: int
+    alive*:       bool
+
+  EnemyTracker* = object
+    enemies*: Table[int, EnemyState]
+
+proc update*(et: var EnemyTracker, botId: int, x, y, heading, speed, energy: float, tick: int) =
+  et.enemies[botId] = EnemyState(id: botId, x: x, y: y, heading: heading,
+                                  speed: speed, energy: energy,
+                                  lastSeenTick: tick, alive: true)
+
+proc markDead*(et: var EnemyTracker, botId: int) =
+  if botId in et.enemies:
+    et.enemies[botId].alive = false
+
+proc resetRound*(et: var EnemyTracker) =
+  et.enemies.clear()
+
+proc getEnemy*(et: EnemyTracker, botId: int): EnemyState =
+  et.enemies[botId]
+
+proc allAlive*(et: EnemyTracker): seq[EnemyState] =
+  for s in et.enemies.values:
+    if s.alive: result.add(s)
+
+proc closestTo*(et: EnemyTracker, x, y: float): EnemyState =
+  var bestDist = Inf
+  for s in et.enemies.values:
+    if not s.alive: continue
+    let d = hypot(s.x - x, s.y - y)
+    if d < bestDist:
+      bestDist = d
+      result = s
+
+proc weakest*(et: EnemyTracker): EnemyState =
+  var bestEnergy = Inf
+  for s in et.enemies.values:
+    if not s.alive: continue
+    if s.energy < bestEnergy:
+      bestEnergy = s.energy
+      result = s

common_libs/targeting/target_selector.nim

@@ -0,0 +1,19 @@
+## Target selector: picks which enemy to aim at.
+
+import enemy_tracker
+
+type TargetMode* = enum
+  tmClosest,   ## nearest enemy
+  tmWeakest,   ## lowest energy (finisher)
+  tmBestGun    ## future — alias to closest for now
+
+proc selectTarget*(et: EnemyTracker, selfX, selfY: float,
+                   mode: TargetMode = tmClosest): int =
+  ## Returns enemy bot ID. Falls back to 1v1 naturally when 1 alive.
+  let alive = et.allAlive()
+  if alive.len == 0: return -1
+  if alive.len == 1: return alive[0].id
+  let chosen = case mode
+    of tmWeakest: et.weakest()
+    else:         et.closestTo(selfX, selfY)  # tmClosest + tmBestGun
+  result = chosen.id