Input API (decouple input from actions, runtime key remapping, multi-device)

Current State

Input is read ad-hoc from SDL directly where needed. There is no abstraction separating raw devices from game actions, no remapping, and no multi-device support.

Goal

A reusable Input API that decouples physical input from semantic actions, supports runtime remapping, and serializes bindings to settings (#13 (closed)).

Tasks

• Raw device layer: keyboard, mouse (move/buttons/wheel), gamepad (axes/buttons/triggers), touch (later)
• Action maps: named actions bound to one or more inputs; button/axis/vector action types
• Polling API (isPressed, wasPressed, axis, vector) and event subscription
• Runtime rebinding (listen-for-next-input) and conflict handling
• Multiple devices / local players (device assignment)
• Serialize/deserialize bindings via the settings/DataAsset system
• Editor UI to view/edit action maps (can reuse #14 shortcut conflict UI)
• Expose to user scripts; wire into examples/basic-project (Player movement)

Acceptance Criteria

• Game code reacts to actions, never raw key codes.
• Bindings can be remapped at runtime and persist across restarts.
• Keyboard + gamepad both drive the same actions.

Related

• #13 (closed) (settings), #14 (shortcuts), #9 (closed) (UI input).