Typography tab persistence

[bph]

Part of #836. Wires the Typography tab. Depends on the Color/foundation PR.

Scope

• TypographySettingsPanel → settings.typography.* (flag fields)
• FontFamiliesPanel → settings.typography.fontFamilies (deepest nested shape — fontFace arrays per family)
• FontSizesPanel → settings.typography.fontSizes

Acceptance criteria

• Adding a font family with multiple fontFace entries persists with the correct nested structure.
• Removing a family removes both the entry and any associated font assets reference (no orphaned assets if theme-fonts.php is involved — confirm during implementation).
• Standard loading / success / error UX.

Out of scope

• Font asset upload / management (existing flow in theme-fonts.php is separate).

References

• Tracking issue: [Tracking] Edit Theme Settings: phased implementation #836