Input: PadRIO -- play without the pod (L4CONTROLS=PAD), Workstream A.1

Ported from RP412: RIOBase split out of the serial RIO (L4RIO.h),
rioPointer is RIOBase* (L4CTRL.h), PAD token -> new PadRIO() speaking
the RIO surface from an XInput pad + keyboard (L4PADRIO/L4PADBINDINGS,
vRIO bindings.txt grammar, hot-plug), KeyLight RGB mirror TU
(BT412KEYLIGHT, /std:c++17 per-file).

BT-side fixes PadRIO forced into the open:
- Both keyboard input bridges (mech4.cpp, mechmppr.cpp BT_KEY_BRIDGE)
  stand down when a RIO device exists -- they overwrote the engine
  controls push every frame. M/X conveniences stay live.
- Mapper attribute chain OFF BY ONE (latent real-pod bug): the DOS
  chain below MechControlsMapper carried two base attributes, WinTesla
  carries one, and AttributeIndexSet::Find is positional -- the .CTL
  stick mapping wrote throttlePosition. Pad slot + binary-locked enum;
  gotcha ledgered (reconstruction-gotchas #11).

Verified: PAD throttle lever ramps + sticks, stick turns with the
authentic speed-vs-turn clamp (61.5 -> 22.0 u/s), mech drives; keyboard
fallback intact (BT_FORCE_THROTTLE harness). New diags: BT_CTRLMAP_LOG,
BT_STICK_LOG. (Phase 2 of docs/BT412-ROADMAP.md)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

content/LAST.EGG

@@ -1,8 +1,8 @@
 [mission]
 adventure=BattleTech
-map=cavern
+map=grass
 scenario=freeforall
-time=night
+time=day
 weather=clear
 temperature=27
 length=600
@@ -156,9 +156,8 @@ x=128
 y=32
 width=8
 [pilots]
-pilot=127.0.0.1:1502
-pilot=127.0.0.1:1602
-[127.0.0.1:1502]
+pilot=200.0.0.96
+[200.0.0.96]
 hostType=0
 advancedDamage=1
 loadzones=1
@@ -172,20 +171,6 @@ dropzone=one
 vehicle=bhk1
 vehicleValue=1000
 color=White
-[127.0.0.1:1602]
-hostType=0
-advancedDamage=1
-loadzones=1
-name=Boreas
-bitmapindex=2
-experience=expert
-badge=VGL
-patch=Yellow
-role=Role::Default
-dropzone=one
-vehicle=ava1
-vehicleValue=1000
-color=Red
 [largebitmap]
 bitmap=BitMap::Large::Aeolus
 [BitMap::Large::Aeolus]
@@ -242,4 +227,3 @@ width=4
 model=dfltrole
 [Role::NoReturn]
 model=noretun
-