Support choosing real fonts for text (not just Carlito styles); fix mislabeled 'Narrow'

[szrudi]

Summary

Text widgets currently expose only four "styles" — regular, bold, italic, narrow — which map to the four bundled Carlito faces in labelle. There's no way to pick an actual font family. We'd like to let users choose real fonts.

Motivation / bug that surfaced this

While reviewing the style options we noticed the "Narrow" option is mislabeled — in labelle's font_config.py the narrow style is wired to Carlito-BoldItalic.ttf:

_DEFAULT_STYLES_TO_FONT_PATH = {
    "regular": ".../Carlito-Regular.ttf",
    "bold":    ".../Carlito-Bold.ttf",
    "italic":  ".../Carlito-Italic.ttf",
    "narrow":  ".../Carlito-BoldItalic.ttf",   # <-- not narrow at all
}

Carlito ships only those four faces (no condensed/narrow variant), so "Narrow" renders bold-italic. Quick mitigation in labelle-web: relabel the dropdown option to "Bold Italic" (keep value="narrow", which is the key labelle expects). The real fix — actual font choice — is this feature.

What labelle already gives us

labelle.lib.font_config.get_font_path() accepts either:

• font= — a font name (resolved from get_available_fonts() = bundled Carlito + matplotlib.findSystemFonts()) or a path to a .ttf, or
• style= — one of the four named styles above.

So the print engine already supports arbitrary fonts; labelle-web simply doesn't surface it.

Proposed work

Backend (server/)

• Add GET /api/fonts wrapping get_available_fonts() (return display names / stems).
• In label_builder.py, when a widget has a font name/path, call get_font_path(font=...) instead of get_font_path(style=...). Define precedence (explicit font overrides style).

Frontend (client/)

• Add optional fontName?: string to TextWidget in types/label.ts.
• Font picker in TextWidgetEditor.tsx populated from /api/fonts.
• Store wiring + save/load .json round-trip.

Constraints to decide up front

• font OR style, not both: get_font_path can't express "Arial + bold" — bold/italic only work if that face is its own file. Combining a chosen family with bold/italic would need an upstream labelle change or per-face selection.
• Fonts in the container: the Docker image ships almost no system fonts, so on the Pi findSystemFonts() will return little. To be genuinely useful this likely needs bundling more fonts and/or a .ttf upload flow (mirroring the existing image-upload path).

Related

• Upstream naming: the narrow style name is a labelle-library misnomer — worth a separate upstream note to labelle-org/labelle.