Investigate motion and hardware-assisted page turning

[mokhov]

Problem

Some native readers support tilt, shake, headset keys, device taps, and other hands-free controls, but browser support and reliability vary widely.

Proposed behavior

Run a bounded capability study and prototype only controls that can be safe and predictable in an installed browser reader.

Acceptance criteria

• Document support for motion sensors, media keys, long-press repeat, and related browser APIs by platform.
• Prototype viable controls behind an explicit experimental flag.
• Permission prompts occur only after a clear user action.
• Selection, accessibility, and accidental activation risks are evaluated.
• Conclude with an implementation recommendation or a documented decision not to ship.