cap terminal reward scale (bounded score bonus) and restore single-battle campaigns

computeRoundReward used cumulative totalScore/50 — unbounded in long battles
(vLoss 353 at round 3160 → 25745 by 3871 in the 5841-round attempt). Cap the
score term at 400 before /50: bonus ∈ [0,8], so the critic's value scale stays
stable regardless of battle length and across battle boundaries.

Reverts the 60-round battle chunking (186e005/da2f825): one battle per
campaign for the whole remaining budget; keeps the crash-restart loop, the
mid-battle freeze guard and the end-of-battle counter completeness check.

Cert (5211, single 60-round battle): 59/60 wins (sole loss = cold-start round
1, score 61), vLoss avg 36.1 / max 148.5, gNorm max 596, zero NaN, zero
restarts, counter check passed. Weights persist to round 5211.

PPO_Bot/tests/test_training.nim

@@ -23,6 +23,9 @@ block testTickReward:
 block testRoundReward:
   let r = computeRoundReward(350.0'f32)
   check abs(r - 7.0'f32) < 1e-6'f32, "computeRoundReward(350) == 7.0, got " & $r
+  # bounded: long-battle cumulative scores must saturate, not blow the value scale
+  check abs(computeRoundReward(89299.0'f32) - 8.0'f32) < 1e-6'f32,
+    "computeRoundReward(89299) == 8.0 (capped), got " & $computeRoundReward(89299.0'f32)
 
 # ── TrajectoryBuffer ──────────────────────────────────────────────────────────