feat(bots): promote gen5 stage-5 policy to the Hard tier

Hard has been a label-only duplicate of medium.json since medium was promoted
on 2026-08-17. Promote 20260823-1734-gen5-s5-intercepts-retry2 into
hard.json so the tier is a genuinely distinct policy, and so the strongest bot
the curriculum has produced survives the next round's checkpoint pruning —
promoted files are never touched by training scripts.

Stage 5 blocked after three attempts, so like medium.json this comes from a run
recorded as decision: "fail". Both failing floors are covered in TRAINING.md:
goal_rate 0.7369 vs 0.75 is marginal, and productive_air_touch_fraction 0.0001
vs 0.005 is a bar no policy in the lineage has approached, against a metric
quantised at 0.01 per ~100-episode window. On every other axis it is the best
yet: upright_fraction 0.757 against a 0.40 floor that the pre-Round-6 lineage
never pushed past 0.331, and forward_motion_fraction 0.479 against 0.20.

Chosen over attempt 2 (retry1) on a tiebreak, not a margin. retry1 posts a much
wider indirect result against medium.json (63-23-14 vs 47-32-21), but a direct
100-episode head-to-head between the two finished 36-39 with 25 draws, so that
gap does not reflect a real strength difference. Attempt 3 is the later
checkpoint (it resumed from attempt 2) and edges every telemetry metric.

Verified: hard.json is byte-identical to its source export, matches easy/medium
on input_size 83, 3 layers and action space, and beats medium.json 19-7-4 in a
fresh 30-episode paired run. Tiers stay monotonic: hard > medium > easy.

That head-to-head also showed a 17% physical side imbalance (physical teams
0-1 = 29-46), reproduced at 13% in the 30-episode check. Inside the 20% bar
used elsewhere and equal across both models, but noted in TRAINING.md as worth
investigating rather than assuming variance.

Game/scripts/main_menu.gd

@@ -13,16 +13,15 @@ const BOTS_DIR := "res://bots"
 
 # Every tier runs its promoted checkpoint at full trained capability —
 # difficulty is a genuinely different policy, never the same policy
-# handicapped with reaction delay or action noise. Easy and Medium are now
-# distinct models (medium.json beats easy.json 65-22-13 head-to-head); Hard
-# still points at medium.json, the strongest promoted policy, and stays a
-# label-only duplicate until a stronger one earns hard.json. Keep the tiers
+# handicapped with reaction delay or action noise. All three tiers are now
+# distinct models: medium.json beats easy.json 65-22-13, and hard.json (the
+# generation-5 Stage-5 policy) beats medium.json 47-32-21. Keep the tiers
 # monotonic: never leave a lower tier pointing at a stronger model than the
 # one above it.
 const DIFFICULTIES := [
 	{"name": "Easy", "model": "res://bots/promoted/easy.json", "reaction_ticks": 8, "action_noise": 0.0},
 	{"name": "Medium", "model": "res://bots/promoted/medium.json", "reaction_ticks": 8, "action_noise": 0.0},
-	{"name": "Hard", "model": "res://bots/promoted/medium.json", "reaction_ticks": 8, "action_noise": 0.0},
+	{"name": "Hard", "model": "res://bots/promoted/hard.json", "reaction_ticks": 8, "action_noise": 0.0},
 ]
 
 @onready var difficulty_dropdown: OptionButton = %DifficultyDropdown