j141 fix: the per-gun real-shot accounting was still array[17] after rack id 17 landed

REGRESSION: the live bot stopped firing entirely and moved degenerately
whenever a rack admitted rack id 17 (the ADE+SBC BITBRAIN gun added in
e9302bc).

ROOT CAUSE: ModularBot.nim declared the per-gun accounting arrays
(gunRealShots / gunRealHits / gunRealShotsByMode / gunRealHitsByMode /
gunSelectionCount) as array[17, int] — the rack size BEFORE id 17 existed.
The instant the selector picked gun 17, the accounting indexed one past
the end:

  * debug build -> IndexDefect out of run(): the bot stops, 0 shots;
  * -d:release (shipped) -> silent out-of-bounds write onto the adjacent
    lastPowerLogKey: string header, so the bot kept moving but never
    fired and never reported a shot.

Measured with the owner's exact out/.env, 1v1 SittingDuck:
  0dc5552 (pre-rename):  BitBrain(id16) selected 356+157 ticks,
                         realShots 24+9, realHits 23+9,  ModularBot wins 180/360
  HEAD (e9302bc..)   :  selected 0, vShots 0, realShots 0, realHits 0
  debug               : IndexDefect on the first tick that selects id 17
  -d:release         : same 0/0/0, bot scores 22 and dies

FIX: derive every gun-indexed width from the rack instead of a literal.
gun_harness/selector exports NumRackGuns* = len(RackGunNames) (18);
ModularBot uses it for the five accounting arrays, the per-round reset
loops, the gun_stats.jsonl dump loop, the  table and
initTracker(). Shipped defaults unchanged: clean env is still the
onlyPattern rack and movement is still strafe.

GUARD: common_libs/tests/test_rack_stat_width.nim (24 checks) — rack
table shape, a source scan proving no gun-indexed width/loop bound is
narrower than NumRackGuns, an in-process accounting replay that would
have overflowed array[17], and the legacy-namespace checks (id 16 via
TR_RACK_BITBRAIN, id 17 never admitted while legacy). It reports 7
failures on the pre-fix ModularBot.nim and passes after. Optional
--live section proves a rack admitting only the newest id fires and
lands hits.

Parity: test_env_report 25, test_rack_membership 49, test_lead_gain_
registration 13, test_lead_gain_legacy 24, test_bitbrain_net 44,
test_gun_harness 39, test_tfil_commit_env 30, test_bitbrain 56,
test_tm_pattern_registration 20 — all unchanged, 0 failures.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

common_libs/gun_harness/selector.nim

@@ -52,6 +52,14 @@ const
     "WALLBOUNCE", "ACCEL", "STOPSHOT", "DISPLACE", "AVGLEAD", "DECAYGF",
     "KNN", "TMSELECT", "TMPATTERN", "TMHORIZON", "LEADGAIN", "BITBRAIN"]
   RackEnvPrefix* = "TR_RACK_"
+  ## THE rack size, derived from `RackGunNames`. Every per-gun-indexed array and
+  ## loop in the bot and in the harness MUST be sized with this, never with a
+  ## literal: adding a gun used to leave the live per-gun real-shot accounting
+  ## at `array[17, int]`, so the newest gun indexed one past the end on the
+  ## first tick it was selected (a hard IndexDefect in a debug build, silent
+  ## memory corruption in `-d:release`). See
+  ## `common_libs/tests/test_rack_stat_width.nim`.
+  NumRackGuns* = len(RackGunNames)
   ## LEADGAIN (id 16) is the per-range-band lead-gain corrector
   ## (`guns/lead_gain.nim`). It USED to be called BITBRAIN; the name now
   ## describes its internals (it learns a multiplier for Pattern's lead per