feat(PPO_Bot): network forward pass + action mapping (#14)

Two-hidden-layer MLP actor-critic (42→64→64→5/1) with stochastic
actorForward, logStd floor at -3, and BotAction mapper wired into
the run() loop. Assert-based test suite covers shapes, finiteness,
logStd collapse, and all action range bounds.

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

PPO_Bot/PPO_Bot.nim

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+## PPO_Bot — enemy tracker + state vector wired into the game loop.
+## Forward pass uses a random ActorCritic policy (weights not yet trained).
+
+import std/os
+import arraymancer
+import tankroyale_botapi
+import network
+import actions
+import ./enemy_tracker
+import ./state_vector
+
+const botJsonPath = currentSourcePath().parentDir / "PPO_Bot.json"
+
+type PPOBot = ref object of Bot
+  tracker: EnemyTracker
+
+var ac = initActorCritic()
+
+method onScannedBot*(bot: PPOBot, e: ScannedBotEvent) =
+  bot.tracker.update(e.x, e.y, e.direction, e.speed, e.energy)
+
+method onRoundStarted*(bot: PPOBot, e: RoundStartedEvent) =
+  bot.tracker = initEnemyTracker()
+
+method run(bot: PPOBot) =
+  while isRunning():
+    bot.tracker.deadReckon()
+
+    setRadarTurnRate(bot.tracker.getRadarTurnRate(
+      getX(), getY(), getDirection(), getRadarDirection()))
+
+    let botData = BotStateData(
+      x:           getX(),
+      y:           getY(),
+      direction:   getDirection(),
+      speed:       getSpeed(),
+      energy:      getEnergy(),
+      gunDirection: getGunDirection(),
+      gunHeat:     getGunHeat(),
+      arenaWidth:  float64(getArenaWidth()),
+      arenaHeight: float64(getArenaHeight()),
+    )
+
+    let state = buildStateVector(botData, bot.tracker)
+    let (rawActs, _) = ac.actorForward(state)
+    let acts = mapActions(rawActs, getSpeed().float32, getGunHeat().float32)
+
+    setTargetSpeed(acts.targetSpeed.float)
+    setTurnRate(acts.turnRate.float)
+    setGunTurnRate(acts.gunTurnRate.float)
+    if acts.shouldFire:
+      discard setFire(acts.firePower.float)
+    go()
+
+when isMainModule:
+  var bot = PPOBot(tracker: initEnemyTracker())
+  start(bot, botJsonPath)