Add background gradients/textures/animations, per-line fonts, foregro…

[jonwilliams84]

…und dividers

Background:

• BoardState.background is now a discriminated union: solid | linear gradient (2 colors + angle) | radial gradient (2 colors).
• DB migration on read maps the old backgroundColor field to { type: "solid", color }, so existing saved state survives.

Effects:

• texture: none | dots | stripes | grid | noise. CSS-only, layered as a translucent ::before so it overlays any background.
• animation: none | pan | pulse | shimmer. pan + pulse drive the texture layer (no-op if texture: none). shimmer is a soft gradient sweep that works regardless of texture.

Dividers:

• Promoted to z-index 3 so they sit on top of letter ascenders, and rebuilt as a translucent dark band + bright lower edge instead of a flat #000 stripe — gives an embossed groove effect that reads on any cell colour without needing to compute a per-row darken().
• Height switched from 0.5rem fixed to 0.6cqh (min 3px) so they scale with the row.

Fonts:

• 6 curated Google Fonts loaded in index.html (Bebas Neue default, Anton, Oswald, Bungee, Permanent Marker, Lobster).
• BoardState.defaultFont sets the board-wide font; Line.font allows optional per-line override.
• New component renders previews of each option in its own family inside the dropdown.

UI:

• Background section in admin replaced with a Background & Effects section using the new BackgroundEditor: type/colors/angle for the background, plus texture and animation pickers.
• New Typography section for the default font.
• LineEditor gains a compact per-line font picker between the text field and the colour swatch; the text field itself renders in the effective font so you can preview without leaving the row.

https://claude.ai/code/session_011pGzV6osudSkwYLZ93A74R