fix(PPO_Bot): radar oscillation, Adam persistence, checkpoint order, channel race

- enemy_tracker: toggle lastOvershootDir each tick; make getRadarTurnRate take var tracker
- training: remove threadvar Adam globals; pass adamStates as var param to ppoUpdate; export ACAdamStates
- PPO_Bot: carry ACAdamStates through TrainingArgs/TrainingResult; drop trainingDone bool and Lock — use resultChan.tryRecv() directly as synchronisation
- weights: sort checkpoint dirs newest-first by mtime instead of hardcoded order
- tests/test_training: pass explicit ACAdamStates to ppoUpdate

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

PPO_Bot/weights.nim

@@ -1,6 +1,6 @@
 ## weights.nim — save/load ActorCritic weights as .npy files.
 
-import std/[os, times, strutils]
+import std/[os, times, strutils, algorithm, sequtils]
 import arraymancer
 import ./network
 
@@ -70,12 +70,21 @@ proc saveCheckpoint*(ac: ActorCritic, weightsRoot: string, roundNum: int) =
     saveWeightsAtomic(ac, weightsRoot / ("checkpoint_" & $slot))
 
 proc loadBestAvailable*(ac: var ActorCritic, weightsRoot: string): bool =
-  ## Try latest/, then checkpoint_3/, checkpoint_2/, checkpoint_1/.
+  ## Try latest/ first, then checkpoints sorted newest-first by mtime.
   ## Returns true if weights loaded, false if all fail (random init stays).
-  for candidate in [weightsRoot / "latest",
-                    weightsRoot / "checkpoint_3",
-                    weightsRoot / "checkpoint_2",
-                    weightsRoot / "checkpoint_1"]:
+  let checkpoints = [weightsRoot / "checkpoint_1",
+                     weightsRoot / "checkpoint_2",
+                     weightsRoot / "checkpoint_3"]
+  # Sort checkpoints newest-first by modification time
+  var existing: seq[tuple[mtime: Time, path: string]]
+  for p in checkpoints:
+    if dirExists(p):
+      existing.add((getLastModificationTime(p), p))
+  existing.sort(proc(a, b: tuple[mtime: Time, path: string]): int =
+    cmp(b.mtime, a.mtime))  # descending
+
+  let candidates = @[weightsRoot / "latest"] & existing.mapIt(it.path)
+  for candidate in candidates:
     if dirExists(candidate):
       var ok = true
       for f in weightFiles: