Add inline controller remap modal and descriptor-based bindings

- Expand `Alt+C` from controller selection to config/remap UI with learn, clear, and reset flows
- Persist full controller binding descriptors through IPC/config (buttons, axes, directions, D-pad fallback)
- Update runtime/tests/docs/config examples for new binding schema; keep `Alt+Shift+C` debug modal

src/shared/ipc/contracts.ts

@@ -19,6 +19,7 @@ export const IPC_CHANNELS = {
     toggleDevTools: 'toggle-dev-tools',
     toggleOverlay: 'toggle-overlay',
     saveSubtitlePosition: 'save-subtitle-position',
+    saveControllerConfig: 'save-controller-config',
     saveControllerPreference: 'save-controller-preference',
     setMecabEnabled: 'set-mecab-enabled',
     mpvCommand: 'mpv-command',