feat: live navigation mode with transit trip-following

[Medformatik]

Summary

Turns the directions panel from a static route previewer into an active, follow-along navigator, plus the supporting infrastructure and a few fixes found while verifying it live.

Live navigation (driving / walking / cycling)

• Navigation engine: a Zustand navigationStore driven by watchPosition through pure, unit-tested functions in packages/core/src/navigation/ (snapToRoute, computeProgress, shouldReroute, nextVoiceCue, processFix). Position is snapped to the route; progress, ETA, and the current maneuver are derived each tick.
• Follow experience: heading-up follow camera (auto-releases on a user pan, restored via a recenter FAB), heading puck, traveled/remaining route split, screen Wake Lock, and locale-aware voice guidance.
• Online reroute when the user leaves the route; arrival detection.
• Maneuver banner, lane guidance, and speed-limit badge, rendered immediately from the static route on Start and refined as GPS fixes arrive (so it works even before/without a fix, with a "waiting for GPS" hint).
• Capability hooks are all feature-detected with graceful fallbacks: useWatchPosition, useWakeLock, useHeading, haptics, platformCapabilities.

Richer routing data

• OSRM and Valhalla adapters now surface normalized maneuver type/modifier, lane guidance, and speed limits on route steps.
• Live speed limit for Valhalla routes via on-the-fly map-matching (/trace_attributes), throttled, for driving.

Settings: measurement units

• New persisted, global metric/imperial preference in the settings panel (alongside language/theme), wired through directions and navigation (distance display + voice). Single source of truth (useSettingsStore); hydrated on the client and no longer clobbered by deep links.

Transit trip-following

• Follow-along mode for a planned transit itinerary: current-leg detection, next stop, stops-until-alight countdown, alight alerts, overall ETA, and current-leg highlighting on the map. No rerouting. Built on the same position primitives.

Navigation UX

• During navigation the map chrome (search, category chips, weather, account avatar, layer selector) is hidden and the directions sidebar collapses; the bottom bar and map controls are positioned clear of the footer.

Fixes found during verification

• Corrected an ioredis defineCommand call in provider-health that passed a stray key-count arg, shifting ARGV and causing all transit plans to 500 with a Lua nil-comparison error.
• Made provider-health recording best-effort so a health-store failure can never fail a user request.
• Gated the ground navigation view to kind=ground so it doesn't overlay transit following.

Notes

• Foreground-only, online navigation. Offline saved-route following is intentionally out of scope.

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