legal: Resolve the Soft Paper palette licensing before commercial distribution

[ebouchut]

Part of #77 (GDPR epic; strictly a licensing topic, kept under the epic to have a single legal backlog).

Context

docs/design/mockups/css/theme-soft-paper.css (the dormant alternate theme) reuses the light palette color values extracted from nickmilo/soft-paper, which is licensed GPL-3.0. Its dark palette is Catppuccin Frappe (MIT: no issue). The default theme (theme-catppuccin.css) is built only from the MIT licensed Catppuccin palette and is unaffected.

Risk

Bare color values are most likely unprotectable facts (a ~15-color selection carries at best thin compilation protection). But if the palette were deemed protectable expression, the stylesheet would be a GPL-3.0 derivative:

• AGPL v3 edition: fine (GPLv3 and AGPLv3 are mutually compatible).
• Commercial edition: blocked (GPL material cannot be relicensed under a proprietary license).

Resolution options (pick one before any commercial distribution)

• Ask Nick Milo for explicit permission (community norm, likely a yes), or
• Drop theme-soft-paper.css (it is unused by design), or
• Re-derive an independent warm-paper palette (the three WCAG-adjusted values are already ours)

No action needed for the certification (academic, non-commercial). Provenance is documented in docs/design/theme-exploration.md and docs/design/mockups/theme-soft-paper-css-explained.md.