Navigation: spoken / audio cues (Maps-style prompts)

[eric-ormoni]

Summary

Add spoken turn-by-turn style prompts during in-app navigation, similar to Apple Maps voice guidance—not only silent on-screen cues.

Motivation

• Safer walks: glance at the phone less often.
• Clearer reassurance at decision points (turns, replans, nearing destination).

Scope (to refine)

• Integrate iOS APIs appropriate for localized speech / route guidance (for example AVSpeechSynthesizer, MapKit / MKDirections-style cues if aligned with how routes are modeled, or CLLocation / step-geometry triggers).
• Respect silent mode, spoken content accessibility settings where applicable, or offer an in-app toggle.
• Pause / duck other audio via AVAudioSession if we mix with music or podcasts.

Acceptance (draft)

• User hears short prompts at meaningful navigation events (examples: imminent turn, off-route hint, nearing end, arrival).
• Prompts can be disabled (or obey system mute) without breaking navigation.
• Document behavior in navigation-related docs (docs/in-app-navigation.md or successor).

Notes

• Depends on the existing plan/nav step model (planLoop, steps, reroutes)—implementation should attach prompts to stable events rather than ad-hoc strings everywhere.