Profiles (keyboard, every gamepad, one controller model) with per-game
overrides keyed by cartridge CRC, SDL3 gamepad auto-detection plus an
optional gamecontrollerdb.txt, "press a button to bind" capture, and a
modal keypad overlay.
The keypad reaches the core through the standard retro_* input API: pad
controls ride the RetroPad bitmask; keypad keys (which have no RetroPad
button for 7, 8, 9, * and #) are synthesised RETRO_DEVICE_KEYBOARD keys on
the keys libretro.c's default path polls, and the host announces a keyboard
after every load so a gamepad-only player is not locked out.
Tests: remap_unit (pure logic) and input_e2e (drives the real core and reads
back the joypad matrix for every control on both ports).
Refs #837
Co-Authored-By: Claude Opus 5.5 <[email protected]>
