feat: event-driven keyboard input (no Input Monitoring needed)

[Periicles]

Why

sfKeyboard_isKeyPressed polls the OS keyboard state. On macOS that returns
false unless the running app has the Input Monitoring permission, so on a
fresh machine movement, attack, interact and Escape all silently did nothing
(mouse-driven menus still worked, which is why it looked like "the keyboard is
dead"). Event-based input only needs window focus, so the game plays anywhere.

What

• New input module: input_handle_event() updates a per-key pressed state from
  the window's KeyPressed / KeyReleased events and clears it on FocusLost;
  is_key_held() reads that state.
• Every sfKeyboard_isKeyPressed(...) is replaced by is_key_held(game, ...)
  (player + raycast movement, attack, NPC interact, the Ctrl-zoom/inventory
  modifier).
• The 2D, raycasting and intro-dialog event loops now call input_handle_event,
  and Escape is handled straight from the event.
• game_t gains a keystate[sfKeyCount] array (zero-initialised).

No keybindings or controls change — only how a held key is detected.

Verification

• make re: warning-free.
• Banana: full project back to 0 findings.
• make tests_run / make tests_asan: 20/20, no ASan/UBSan findings.

Please test (behaviour change)

This changes the input model, so a quick play is worth it:

• Movement (arrows / ZQSD after switching layout), attack, talking to NPCs (E),
  Escape to open/close the pause menu, Ctrl+wheel zoom.
• Ideally confirm it now works without granting Input Monitoring (the original
  symptom).