j147 results: 180-battle live A/B on the frozen 15-opponent panel

Within-mover references (the only comparison that isolates the knob): tfil_lag1
-0.04 wins/run, strafe_lag1 +0.18 wins/run, both far under the reported MDEs
(0.33 / 0.41) -> NOT distinguishable, so TR_FIRE_LAG stays default 0. Incoming
hit rate also unmoved (+0.94 / +0.33 pp). The one significant result is the
mover (strafe_lag1 vs tfil_off +0.38 wins/run p=0.0386, hit rate -4.67pp
p=0.0074), which is the known strafe-over-tfil gap and exactly why the
within-mover reference was pre-registered.

Also a cosmetic no-op refactor of the two spawn sites (compute velX/velY once;
bit-identical, and it keeps the default-parity claim exact).

common_libs/movements/the_floor_is_lava.nim

@@ -433,16 +433,18 @@ proc spawnTrackedWave(m: var TFILModule, ws: WorldState, ei: EnemyInfo,
     m.bullets.del(0)  # ponytail: drop oldest; fine for 20-bullet cap
   # j147: back-date the shot by the measured detection lag (`TR_FIRE_LAG`,
   # default 0 = untouched).  See `movement_harness/fire_tracker.nim`.
+  let vx = speed * cos(heading)
+  let vy = speed * sin(heading)
   var gx = ei.x
   var gy = ei.y
   if FireLag > 0:
-    gx += (speed * cos(heading)) * FireLag.float
-    gy += (speed * sin(heading)) * FireLag.float
+    gx += vx * FireLag.float
+    gy += vy * FireLag.float
   m.bullets.add TrackedBullet(
     originX: ei.x, originY: ei.y,
     x: gx, y: gy,
-    velX: speed * cos(heading),
-    velY: speed * sin(heading),
+    velX: vx,
+    velY: vy,
     power: power,
     alive: true,
     age: 0)