[Nomad FR]: Import weather from Spotwx API (with API key)

[spydmobile]

What is needed?

Direct integration with the Spotwx API using a configurable API key, so users can pull forecasts into Nomad without manual file export/import.

Scope (future sprint)

• User supplies a Spotwx API key (Settings modal, similar to CFS API key).
• Weather import step gains a "Fetch from Spotwx" option alongside file upload.
• Request coordinates derived from the location step; response normalized into Nomad's internal weather schema.
• Error surfaces: invalid key, rate limit, no coverage at location.

Dependencies

• File-based Spotwx import must land first (parser + normalization reusable).
• API key management pattern from existing CFS integration (SettingsModal.tsx).

Out of scope for this issue

• Caching, offline fallback, batch fetching multiple locations.