fix(input): keys are physical positions on every layout; Input.key_label names them

The Windows runtime keyed the held set by the character MapVirtualKeyA gave a
virtual key, so a game's WASD belonged to whatever the active layout put there,
and with an input method on every letter arrived as VK_PROCESSKEY. The typing
block is now read from the scancode (the arrows, numpad and F-keys still by
virtual key); macOS reads keyCode the same way. Input.key_label(key) names a key
in the player's own layout (Windows) or as its US character elsewhere.

Verified on Windows with SendInput into a live window: VK_Z carrying W's scancode
holds 'w', VK_PROCESSKEY carrying A's holds 'a', Caps Lock changes nothing.

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

examples/library/input_key_label.ludic

@@ -0,0 +1,24 @@
+# input_key_label.ludic — the name a player sees for a key. Letters, digits and
+# punctuation are physical positions named for the US layout; headless the label is that
+# character upper case, and the named keys and arrows are words. An unnamed code is "".
+#
+# Deterministic; a full run prints:  W A ; 1 Space Esc Shift Left Right 0 1
+program InputKeyLabel {
+  function bi(b: bool) -> int { if b { return 1 };  return 0 }
+
+  entry {
+    print(Input.key_label('w'))
+    print(Input.key_label('a'))
+    print(Input.key_label(';'))
+    print(Input.key_label('1'))
+    print(Input.key_label(32))
+    print(Input.key_label(27))
+    print(Input.key_label(16))
+    print(Input.key_label(Key.Left))
+    print(Input.key_label(Key.Right))
+    print(len(Input.key_label(200)))
+    Input.press('a')
+    Input.poll()
+    print(bi(Input.key_down('a')))       # the held set is unchanged by naming
+  }
+}