feat: Add Pirate Weather API key to onboarding wizard and portable setup

[Orinks]

Summary

The Pirate Weather provider was added in #477, but it is not yet integrated into the onboarding wizard or portable setup flows. Users need a way to configure the PW API key during first-run setup and in portable mode.

What Needs Updating

1. Onboarding Wizard

• Add a Pirate Weather API key step alongside the existing Visual Crossing key step
• Include a link to https://pirateweather.net/ for free key signup
• Allow skip (key is optional, just like VC)

2. Onboarding Readiness Summary

Currently shows:

• Location configured
• OpenRouter key set
• Visual Crossing key set

Should also show:

• Pirate Weather key set: Yes/No

3. Portable Setup Hint Dialog

Currently says:

"Visual Crossing weather provider keys can be entered in Settings > Data Sources."

Should mention Pirate Weather too:

"Visual Crossing and Pirate Weather provider keys can be entered in Settings > Data Sources."

4. Portable API Key Export/Import

Verify pirate_weather_api_key is included in PORTABLE_API_SECRET_KEYS for encrypted bundle export/import.

References

• Pirate Weather provider: PR feat: Add Pirate Weather with full integration (#477, #481, #482, #483) #479
• Onboarding code: app.py (_maybe_show_first_start_onboarding, _show_onboarding_readiness_summary)
• Portable hint: app.py (_maybe_hint_portable_keys)