j144 TFIL: arrival-based commitment + hysteresis + no mid-flight reversal

The owner's live-GUI report was correct on all four counts, and all four are
one bug: the commitment is cancelled by our own tile-boundary crossing
(96.1% of picks, 3793/3946, mean hold 5.06 ticks) while the bot is still
accelerating, and the picker is an unconstrained uniform draw over every
safe tile, so the new target can land in the mirror direction at |speed| < 4.

New knobs, all env-gated and default = today's behaviour (byte-for-byte
default parity guard re-run and green, 51 checks):
  TR_TFIL_COMMIT_ARRIVAL  hold the committed tile until we are ON it; the
                          tick knob becomes a MINIMUM dwell. 0 = shipped.
  TR_TFIL_COMMIT_MARGIN   leave only if the best alternative is at least
                          this much cooler on the same pathMaxHeat scale.
                          0 = shipped.
  TR_TFIL_NOREV_SPEED     while |speed| is below this, a mid-flight switch
                          may not take a tile >90 deg off the travel
                          direction. 0 = shipped. norevPool() never returns
                          an empty pool: with every candidate behind us it
                          takes the least-bad turn.

Offline gate (recorded DrussGT fixture, 20026 ticks): mean hold 4.1 -> 24.0
ticks, abandoned-before-arrival 92.8% -> 40.5%, committed tile actually
reached 3.3% -> 17.2%, opposite-direction slow mid-flight switches 394 -> 64
(-84%). 'TR_TFIL_TILE_REPLAN=off' alone - what cc11ede's arm B already tried -
only gets the hold to 13.6, which is why that A/B could not find this.

strafe is untouched: it imports only heatDecay/bulletMagScale/Pillar*, none
of which this touches. TR_MOVEMENT default stays strafe. Registered in
env_report.nim + knownEnvNames() + .env.example. Arms pre-registered in
docs/movement_campaign.md and tools/ab/arms_tfil_commit.txt.

ModularBot_garage/.env.example

@@ -111,6 +111,9 @@ TR_TFIL_TILE_REPLAN=self    # self | enemy | off: when a dodge commitment is can
 TR_TFIL_COMMIT_TICKS=15      # ticks to commit to a dodge point before replanning
 TR_TFIL_NO_REV=off      # on = never reverse direction inside a corridor
 TR_TFIL_COMMIT_LOG=     # path for the per-commit log; empty = no log
+TR_TFIL_COMMIT_ARRIVAL=off   # on = hold the dodge tile until we are ON it (not a fixed dwell)
+TR_TFIL_COMMIT_MARGIN=0.0    # lava an alternative tile must be cooler by before it wins the tile
+TR_TFIL_NOREV_SPEED=0.0      # px/tick; below this, a mid-flight switch may not turn the bot around
 TR_TFIL_HEAT_TIME=off   # on = index bullet heat by time (flat field when off)
 TR_TFIL_HEAT_TAU=9.0    # ticks a tracked bullet's heat lives for
 TR_TFIL_HEAT_POWER_GAIN=1.0  # scale of the heat a bullet paints, per firepower