fix(training): restore ground_tilt_penalty, add grounded_upright_fraction diagnostic

Round 4 changed three things at once and two of them cut upright pressure:
grounded_upright_reward went to 0 and ground_tilt_penalty was cut 2.5x,
while the new uprightness multiplier only pays below GROUND_HANDLING_HEIGHT
*and* while moving forward *and* facing the ball - a far narrower slice of
ticks than the penalty it was meant to replace. Net pressure fell and
upright_fraction fell with it (0.268 -> 0.239 -> 0.238, the lowest of any
round). Restore ground_tilt_penalty to 0.05 and change nothing else, so
this is a genuine single-variable test of multiplier plus full tilt
pressure.

The conjunctive mechanism itself held up: forward_motion_fraction reached
its best sustained value (0.242) without goal_rate sagging, ep_rew_mean
turned positive for the first time (+0.28), and eval win rate hit 49% with
no reward hacking.

Also adds grounded_upright_fraction: a diagnostic, deliberately ungated
metric measuring uprightness over real floor-contact ticks instead of
sub-3m ticks. upright_fraction has never exceeded 0.331 across four rounds
and ~560M steps without cheating, and its denominator is dominated by
ballistic transit (airborne_fraction ~0.45, mean_altitude ~4.4m) where
attitude is not meaningfully controllable - so it likely cannot measure
what the 0.45 floor was meant to capture. Re-baseline that floor from what
this reports rather than from another round of reshaping.

training/train.py

@@ -69,7 +69,14 @@ class FlightTelemetryCallback(BaseCallback):
     24h+ run later, which is what made every past generation's failure mode
     expensive to diagnose. Requires VecMonitor(..., info_keywords=(...,
     "airborne_fraction", "mean_altitude", "air_touch_fraction",
-    "vertical_thrust_mean")) — see ShipAIController.get_info."""
+    "vertical_thrust_mean")) — see ShipAIController.get_info.
+
+    grounded_upright_fraction is diagnostic only and deliberately ungated:
+    upright_fraction's denominator is sub-3m ticks, most of which are
+    ballistic transit rather than driving, so it understates uprightness
+    while the ship is actually on the floor. Adding a key here requires
+    adding it to VecMonitor's info_keywords below too, or the bare
+    info[key] lookup raises KeyError mid-run."""
 
     _KEYS = (
         "airborne_fraction",
@@ -79,6 +86,7 @@ class FlightTelemetryCallback(BaseCallback):
         "productive_air_touch_fraction",
         "upright_fraction",
         "forward_motion_fraction",
+        "grounded_upright_fraction",
     )
 
     def _on_step(self) -> bool:
@@ -448,6 +456,7 @@ def main():
             "productive_air_touch_fraction",
             "upright_fraction",
             "forward_motion_fraction",
+            "grounded_upright_fraction",
         ),
     )