fix(worker): normalize map coordinates to WGS84

[SajoLuo]

What changed

• Keep the Worker UI's internal coordinates in WGS84.
• Convert Amap layer clicks, drags, marker positions, and map centers between GCJ-02 and WGS84.
• Normalize direct Apple Maps and Amap coordinates before saving them to the device.
• Move the existing Worker conversion functions into a shared coordinate module and add browser/runtime regression tests.

Why

The server-side parser already converted mainland Apple Maps and Amap coordinates to WGS84, but the web page treated every map layer and pasted coordinate as WGS84. Amap tiles use GCJ-02, so selecting a point on that layer or pasting a mainland Apple/Amap URL saved an offset coordinate. Switching between Amap and WGS84 layers could also move the visible center and marker.

Impact

• Mainland map selections and pasted Apple/Amap coordinates no longer drift after being written to WLOC.
• Switching layers keeps the same physical map location.
• WGS84 layers, raw WGS84 coordinates, and coordinates outside mainland China keep their existing behavior.

Validation

• cd worker && node --test (5 tests)
• npx wrangler deploy --dry-run --minify
• Loaded the minified Worker bundle, compiled its generated inline page script, and verified a public Apple Maps sample resolves to the expected WGS84 coordinate.
• Confirmed the coordinate correction on-device.