Switch icons from a webfont to self-hosted SVG masks — the webfont was the actual problem

Self-hosting Font Awesome's font files (previous commit) didn't fix it either: every icon in the picker still failed identically. That rules out CDN/network blocking specifically and points to something in the browser blocking custom webfont loading altogether regardless of origin (common with strict anti-fingerprinting protection, e.g. Brave's font blocking or certain privacy extensions — @font-face loading is a well-known fingerprinting vector).

Replaced the whole mechanism: each of the 258 curated icons is now a real downloaded SVG file (static/icons/*.svg, sourced from Font Awesome 5 Free's official SVG package) displayed via CSS mask-image (.icon-svg in style.css) instead of a font glyph. A masked SVG isn't a font resource at all, so it isn't subject to webfont-blocking — and it still colors via the existing "color" style property (background-color:currentColor) and sizes via font-size (1em), so no change to how the widget's other controls work.

The "Icône" widget now stores just the icon's slug (e.g. "trophy") in a dedicated attribute instead of a full CSS class string, rendered by a new special_render (render_icone.py). Updated the add-gallery and the properties-panel picker modal to use the same mask technique for their previews, and element_add.py to validate the slug against the curated list. Removed the now-unused self-hosted Font Awesome CSS/webfont files and the <link> tags — no font dependency left for icons at all.

Verified end to end (gallery renders with real SVG previews, simulated add creates a correctly-attributed element, the SVG file is actually served, the per-element picker reflects the current icon). Full suite green (89).

static/icons/otter.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 640 512"><!-- Font Awesome Free 5.15.4 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) --><path d="M608 32h-32l-13.25-13.25A63.97 63.97 0 0 0 517.49 0H497c-11.14 0-22.08 2.91-31.75 8.43L312 96h-56C149.96 96 64 181.96 64 288v1.61c0 32.75-16 62.14-39.56 84.89-18.19 17.58-28.1 43.68-23.19 71.8 6.76 38.8 42.9 65.7 82.28 65.7H192c17.67 0 32-14.33 32-32s-14.33-32-32-32H80c-8.83 0-16-7.17-16-16s7.17-16 16-16h224c8.84 0 16-7.16 16-16v-16c0-17.67-14.33-32-32-32h-64l149.49-80.5L448 416h80c8.84 0 16-7.16 16-16v-16c0-17.67-14.33-32-32-32h-28.22l-55.11-110.21L521.14 192H544c53.02 0 96-42.98 96-96V64c0-17.67-14.33-32-32-32zm-96 16c8.84 0 16 7.16 16 16s-7.16 16-16 16-16-7.16-16-16 7.16-16 16-16zm32 96h-34.96L407.2 198.84l-13.77-27.55L512 112h77.05c-6.62 18.58-24.22 32-45.05 32z"/></svg>