Add settings page for managing forecasting API key and URL via UI

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/node_modules/d3-format/README.md

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+# d3-format
+
+<a href="https://d3js.org"><img src="https://github.com/d3/d3/raw/main/docs/public/logo.svg" width="256" height="256"></a>
+
+This module formats numbers for human consumption, with a consistent output allowing comparison. Grouped digits, currencies, scientific notation…
+
+## Resources
+
+- [Documentation](https://d3js.org/d3-format)
+- [Examples](https://observablehq.com/@d3/d3-format)
+- [Releases](https://github.com/d3/d3-format/releases)
+- [Getting help](https://d3js.org/community)