j165: port tfil's arrival commitment to tfil_ring, default off

The_floor_is_lava_ring carried raw commitTicks with no arrival guard and no
no-reversal guard. Port the behaviour of tfil's j144 fix on RING-SPECIFIC env
names (TR_TFIL_RING_COMMIT_ARRIVAL, TR_TFIL_RING_NOREV_SPEED) so the two forks
never share a namespace. Both default OFF: with them unset the ring mover is
byte-for-byte the pre-change mover over the whole 20026-tick fixture replay
(golden generated from git show HEAD:..., checked by tfil_ring_replay.nim).

Structural differences from tfil, all noted in the code:
  * ring has no TfilTileReplanMode - the tile-crossing cancel is unconditional
    self-tile, so the arrival guard is just 'not TfilRingCommitArrival'.
  * ring has no replanReason enum, so the arrival/danger/expiry outcomes are a
    local bool; the default-off path keeps ring's original dec/no-dec exactly.
  * ring's MinCommitTicks is 0 (tfil's is 5), so the arrival branch is evaluated
    from the first committed tick. Left as is: changing it would change the
    default path.
  * ring's ScoredTile carries no turnDeg, so the no-reversal offsets are
    computed by ringTileOffTravel at the pick site.
TR_TFIL_COMMIT_MARGIN (tfil's hysteresis) is deliberately NOT ported: it is a
third knob, outside the two named, and inert at its 0.0 default.

No other tfil mechanism touched: no turn-cost tiebreak, TR_TFIL_ARRIVE_TICKS,
TR_FIRE_LAG, heat-field override, corridor bound, hold, or geometry weighting.
No default changed anywhere.

ModularBot_garage/.env.example

@@ -104,6 +104,8 @@ TR_TFIL_RANGE_LO=100.0   # px; lower edge of the range band the ring mover prefe
 TR_TFIL_RANGE_HI=200.0   # px; upper edge of that band
 TR_TFIL_RANGE_TEMP=0.4   # sharpness of the ring mover's weighted random draw
 TR_TFIL_RANGE_K=60.0     # px; how fast the weight falls off outside the band
+TR_TFIL_RING_COMMIT_ARRIVAL=off  # tfil_ring only: on = hold the dodge tile until we are ON it (not a fixed dwell)
+TR_TFIL_RING_NOREV_SPEED=0.0     # tfil_ring only; px/tick; below this, a mid-flight switch may not turn the bot around
 TR_TFIL_CORRIDOR_HEAT=10.0   # lava painted per corridor-overlapping tile
 TR_TFIL_CORRIDOR_TICKS=0.0    # corridor length in ticks: 0 = to the wall (shipped); N>0 = min(to wall, bullet speed * N)
 TR_TFIL_WALL_HOTNESS=15.0    # peak heat painted on tiles next to a wall