Add pirateweather.net backend

[Copilot]

Implements the pirateweather.net weather backend (finishing PR #194), fixing several bugs in the original before merging.

Motivation and Context

Adds support for pirateweather.net as a weather data backend. The original PR had correctness bugs and unfinished code that prevented it from being merged.

Description

Bug fixes from original PR:

• Unit conversions (all wrong in original): precipIntensity mm/h → m/h (÷1000), visibility km → m (×1000), windSpeed/windGust m/s → km/h (×3.6) — SI units from the API require all three conversions
• toForecast refactor: replaced 7 copy-pasted if numdays > N blocks (each with a stray log.Println("1") debug statement) with a loop grouping hourly data by day boundary; also fixed month-boundary detection using year+month+day comparison instead of day-of-month only
• Debug logging: json.MarshalIndent(body, ...) on a []byte emits base64, not JSON — replaced with string(body); API key redacted from logged URL
• Error handling: panic() → log.Fatal() to match other backends; added missing API key presence check
• JSON parsing: flags.nearest-station and elevation changed from uint to int — the API returns -999 as a "not implemented" sentinel for nearest-station, and elevations can be negative (below sea level locations)

Code style:

• All exported type names lowercased (PirateweatherConfig → pirateweatherConfig, etc.) to match conventions in other backends

Documentation:

• Added pirateweather to the backends list in the Features section of README.md
• Added a new Pirateweather configuration section to README.md under Backends, with a link to sign up for a free API key and a sample .wegorc config

Steps for Testing

Obtain a free API key from pirateweather.net and run:

wego -backend pirateweather.net -pirateweather-api-key <KEY> -location "lat,lon"

Test with -pirateweather-debug flag to verify debug output doesn't expose the API key and correctly prints the JSON response body.

Screenshots

[kordianbruck]

@copilot add a section to the README.md for how to configure pirateweather. Ensure any other documentation is up to date.

[Copilot]

@copilot add a section to the README.md for how to configure pirateweather. Ensure any other documentation is up to date.

Done in f180c4a. Added pirateweather to the backends list in the Features section and added a new configuration block under the Backends section with signup link, example .wegorc config, and a note that location must be specified as lat,lon coordinates.

[kordianbruck]

@copilot resolve any lint issues and also investigate/resolve this parsing mistake: "2026/04/12 00:59:18 Failed to unmarshal pirateweather response: json: cannot unmarshal number -999 into Go struct field .flags.nearest-station of type uint"

[Copilot]

@copilot resolve any lint issues and also investigate/resolve this parsing mistake: "2026/04/12 00:59:18 Failed to unmarshal pirateweather response: json: cannot unmarshal number -999 into Go struct f...

Fixed in 3d38283. The nearest-station field in the Flags struct was typed as uint, but the Pirateweather API returns -999 as a "not implemented" sentinel value. Changed it to int. Also changed Elevation from uint to int since heights above sea level can be negative (e.g. Death Valley). No lint issues found (go vet and go build both pass cleanly).