BitBrain gun (id 16): Pattern-relative ADE+SBC aim corrector, default off

Wire the verified common_libs/bitbrain ADE+SBC library into ModularBot as a
fine-grained angular corrector on top of Pattern's prediction, the shape the
offline gate test measured (argmax readout over N correction classes).

- common_libs/guns/bitbrain_gun.nim: new gun. Input = the existing TMHorizon
  53 bits (tmhBaseBits + tmhLits); output = argmax class centre over
  +-TR_BITBRAIN_RANGE, applied by rotating the Pattern point around the shooter
  exactly as tmhApplyShift does. Label = the +h-tick fact from TmHorizonGun's
  own observation ring (never across a round). Prequential (defer + resolve).
  AD layer synthesised online for our binary inputs (center=0): heuristic
  cold-start thresholds + running-histogram ~1% percentile init + the library's
  adaptThresholds. Memory modes perRound (default, measured best) / retained /
  decay (periodic partial SBC wipe). Lazy network build + local RNG, so the
  default path builds nothing and consumes no global randomness.
- tm_horizon.nim: export tmhUpdateHistory and add tmhObservedAt (label seam).
- selector.nim: register BITBRAIN at rack id 16, default rmOff, in the SAME
  commit as the id and the wiring (the aed579b admission bug is not repeated).
- ModularBot.nim: id 16 wired through predict/spawn/onResult/resets/colors,
  arrays grown 16->17, spawn gated on rack admission, per-round/per-battle/
  target reset hooks.
- env_report.nim: report every TR_BITBRAIN_* knob + add names to the known set.
- tests: update the rack length literals; new test_bitbrain_registration
  (default-parity: off, lazy, global-RNG clean).

Guard counts unchanged: rack 48, tm_pattern_registration 20, vbullet_admit 12,
env_report 25, and the rest of the suite green.

common_libs/tests/test_tm_pattern_registration.nim

@@ -62,7 +62,7 @@ proc seedOldRack(t: var VirtualTracker, targetId: int) =
 # ── registration table ────────────────────────────────────────────────────────
 
 proc testTable() =
-  check "rack: RackGunNames has 16 entries", RackGunNames.len == 16
+  check "rack: RackGunNames has 17 entries", RackGunNames.len == 17
   check "rack: the new gun is named TMPATTERN at id 14",
         RackGunNames[TmPatternId] == "TMPATTERN"
   check "rack: the new gun defaults to `off`",
@@ -82,9 +82,9 @@ proc oldRackMembership(): array[15, RackMembership] =
 
 proc testDefaultAdmitsOnlyPattern() =
   check "default membership admits only PATTERN (1v1)",
-        admittedGuns(15, rm1v1, DefaultRackMembership) == @[PatternId]
+        admittedGuns(17, rm1v1, DefaultRackMembership) == @[PatternId]
   check "default membership admits only PATTERN (melee)",
-        admittedGuns(15, rmMelee, DefaultRackMembership) == @[PatternId]
+        admittedGuns(17, rmMelee, DefaultRackMembership) == @[PatternId]
 
 proc testEnvOverride() =
   for name in RackGunNames: delEnv("TR_RACK_" & name)