Mouse buttons are bindable; mouse LOOK scoped (not built)

BUTTONS (shipped).  Win32 hands mouse buttons out as virtual keys, and the
binding path already stores VKs and polls GetAsyncKeyState -- so this needed no
verb, no parser change and no new machinery, just names:

    key MOUSE4 button 0x40        # side buttons
    key MOUSE5 button 0x46
    key MOUSEMIDDLE button 0x41

MOUSELEFT/MOUSERIGHT are named too, with a warning in the file header and the
docs: they are how the player presses cockpit buttons (left = press, right =
latch), and the poll is focus-guarded but not click-aware, so binding either
ALSO fires on every panel click.  The side and middle buttons are the free
ones.  Axes work as well (`key MOUSE4 axis Throttle slew + 0.7`).

One guard: the RGB lamp mirror skips mouse VKs when building its map -- a
keyboard lamp array has no mouse buttons to paint (BTPadBindingIsMouseKey).

Verified live: a bindings.txt carrying two mouse rows loads 76 keys (74 + 2),
and a real injected XBUTTON1 press produced `[emitter] FIRED #1`.  Clean A/B --
the earlier run whose SendInput failed the struct-size check logged no fire at
all.  Shipped commented-out examples in the default profile so the capability
is discoverable.

LOOK (scoped only).  docs/MOUSELOOK_PLAN.md.  Mouse MOVEMENT is a real feature,
not a table entry, and the hard part is not reading the device:

 - The cursor is already spoken for.  The glass cockpit's premise is that all
   72 buttons are mouse targets; mouse-look wants a captured, hidden, recentred
   cursor.  Both cannot be true, so this is a MODE question first -- four
   models compared, recommending hold-to-look (costs nothing when unbound,
   cannot strand a player, behaves the same in surround and exploded layouts).
 - The channels are POSITIONAL (JoystickX/Y are -1..1 deflections the mapper
   reads per control mode); a mouse gives deltas.  Accumulate-into-a-virtual-
   stick reuses every existing rule; a rate model would need new mapper
   semantics.
 - Control mode changes what it MEANS: BASIC steers with the stick, MID/ADV
   twist the torso -- so mouse-look steers in one and aims in the other.

Proposed grammar (new row type, so old builds skip it with a warning),
where the code goes, ~250 lines, and a verification plan whose load-bearing
item is "panel clicks still work when a mouselook binding exists but is not
engaged".  Also flagged: the pod had NO mouse, so nothing here is
reconstruction -- every choice is design, judged on feel, and it must stay out
of the pod build's path.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

engine/MUNGA_L4/L4PADBINDINGS.cpp

@@ -61,8 +61,42 @@ static const NamedValue keyNames[] =
 	{ "BACKTICK",	VK_OEM_3 },		{ "LBRACKET",	VK_OEM_4 },
 	{ "BACKSLASH",	VK_OEM_5 },		{ "RBRACKET",	VK_OEM_6 },
 	{ "QUOTE",		VK_OEM_7 },
+	//
+	// MOUSE BUTTONS (2026-07-26).  Win32 hands these out as virtual keys, and
+	// the whole binding path already stores VKs and reads them with
+	// GetAsyncKeyState -- so they need no verb, no parser change and no new
+	// machinery, just a name.  `key MOUSE4 button 0x40` works exactly like any
+	// other key row, axes included.
+	//
+	// ⚠ MOUSELEFT/MOUSERIGHT are how the player presses cockpit buttons (left
+	// = press, right = latch).  The poll is focus-guarded but not click-aware,
+	// so binding either ALSO fires on every panel click.  They are named here
+	// for completeness; the middle and side buttons are the free ones.
+	//
+	{ "MOUSELEFT",	VK_LBUTTON },	{ "MOUSERIGHT",	VK_RBUTTON },
+	{ "MOUSEMIDDLE", VK_MBUTTON },
+	{ "MOUSE4",		VK_XBUTTON1 },	{ "MOUSE5",		VK_XBUTTON2 },
+	{ "MOUSEX1",	VK_XBUTTON1 },	{ "MOUSEX2",	VK_XBUTTON2 },
 };
 
+//
+// A mouse button rather than a keyboard key?  (Used where a binding only
+// makes sense for a real key -- the RGB lamp mirror, which paints keycaps.)
+//
+static int
+	IsMouseVirtualKey(int virtualKey)
+{
+	return (virtualKey == VK_LBUTTON || virtualKey == VK_RBUTTON ||
+			virtualKey == VK_MBUTTON || virtualKey == VK_XBUTTON1 ||
+			virtualKey == VK_XBUTTON2) ? 1 : 0;
+}
+
+int
+	BTPadBindingIsMouseKey(int virtualKey)
+{
+	return IsMouseVirtualKey(virtualKey);
+}
+
 static const NamedValue padButtonNames[] =
 {
 	{ "A",			XINPUT_GAMEPAD_A },
@@ -202,6 +236,10 @@ static const char *defaultProfileText =
 "#   key     <KEYNAME> axis <channel> set <value>            jump/detent\n"
 "#   pad     <PADBTN>  button <addr>\n"
 "#   padaxis <PADAXIS> axis <channel> [invert] [slew <rate>]\n"
+"# <KEYNAME> may be a MOUSE BUTTON: MOUSEMIDDLE, MOUSE4, MOUSE5 (the two\n"
+"#   side buttons; MOUSEX1/MOUSEX2 are aliases).  MOUSELEFT and MOUSERIGHT\n"
+"#   also work but are how you press cockpit buttons -- bind them and they\n"
+"#   fire on every panel click too.  Mouse MOVEMENT is not bindable.\n"
 "# Channels: Throttle JoystickX JoystickY LeftPedal RightPedal Turn\n"
 "#   (Turn = signed composite: + drives the right pedal, - the left --\n"
 "#    made for mapping a gamepad stick to turning)\n"
@@ -240,6 +278,10 @@ static const char *defaultProfileText =
 "key RALT button 0x3F\n"
 "\n"
 "# --- the four mappable fire buttons ------------------------------------\n"
+"# The mouse's side buttons are free if you want them on the trigger:\n"
+"#   key MOUSE4 button 0x40\n"
+"#   key MOUSE5 button 0x46\n"
+"#   key MOUSEMIDDLE button 0x41\n"
 "key SPACE   button 0x40   # main trigger\n"
 "key NUMPAD0 button 0x40   # main trigger\n"
 "key NUMPAD1 button 0x45   # pinky\n"

engine/MUNGA_L4/L4PADRIO.cpp

@@ -230,6 +230,14 @@ PadRIO::PadRIO():
 				{
 					continue;
 				}
+				// A keyboard lamp array has no mouse buttons to paint.
+				{
+					extern int BTPadBindingIsMouseKey(int virtualKey);
+					if (BTPadBindingIsMouseKey(binding.virtualKey))
+					{
+						continue;
+					}
+				}
 				Logical duplicate = False;
 				for (int j = 0; j < count; ++j)
 				{