[medium] Zero refresh intervals are still polled every five seconds

[MeyerThorsten]

Severity: medium
Category: performance

A refresh interval of 0 currently means "update on every scheduler tick" instead of "self-managed / no polling".

Evidence:

• src/main.ts:80 registers TrafficLayer with interval 0.
• src/main.ts:85 registers PlacesLayer with interval 0.
• src/layers/layer-manager.ts:93-98 runs layer.update() whenever now - meta.lastUpdate >= meta.interval, which is always true for 0.
• src/layers/places-layer.ts:91-118 performs a live nearby-places API request inside update().

Impact:

• self-managed layers still poll every 5 seconds
• this burns API quota and increases rate-limit risk while the app is idle
• unnecessary requests also add avoidable UI and network churn

Recommended fix:

• treat 0 or negative intervals as manual-only and skip them in the scheduler
• or add an explicit auto-refresh flag instead of overloading the interval value