Add custom heading and body font settings

[HarshankPatel9038]

PR Summary

Adds optional custom heading and body font settings. Merchants can use either a Google Fonts stylesheet URL or a direct WOFF2 font URL without editing theme code.

Why are these changes introduced?

Dawn currently supports Shopify's font picker for typography. This change gives merchants an opt-in way to use custom brand fonts while preserving the existing font picker as the default experience.

What approach did you take?

• Added separate opt-in settings for custom heading and body fonts.
• Added fields for font family, font URL, weight, and style.
• Created a reusable custom-fonts snippet that:
  • Loads Google Fonts stylesheet URLs.
  • Defines @font-face for direct WOFF2 URLs.
  • Uses font-display: swap.
• Updated both theme.liquid and password.liquid so custom fonts apply consistently across the storefront and password page.
• Preserved the existing Dawn font-picker behavior whenever custom fonts are disabled.
• Added schema translations for all supported Dawn schema locales.

Other considerations

• This is fully opt-in and does not change the appearance of existing themes after upgrade.
• A Google Fonts URL requires the configured font-family value to match the family provided by the stylesheet.
• Direct font URLs are expected to point to WOFF2 files.

Decision log

#	Decision	Alternatives	Rationale	Downsides
1	Keep Shopify font picker as the default	Replace the existing font picker	Prevents visual changes for existing merchants	Adds additional typography settings
2	Support Google Fonts stylesheet and direct WOFF2 URLs	Support only one source type	Supports common merchant font workflows	Merchants must provide a valid URL
3	Use font-display: swap	Default font-loading behavior	Avoids invisible text while custom fonts load	A brief fallback-font render can occur

Visual impact on existing themes

None by default. Existing themes retain their current selected heading and body fonts. Custom fonts are applied only after a merchant enables the relevant setting.

Testing steps/scenarios

• Ran shopify theme check --path .
• Validated updated Liquid, schema, locale, and snippet files.
• Enable a custom heading Google Fonts stylesheet and verify headings use the configured font.
• Enable a custom body Google Fonts stylesheet and verify body text uses the configured font.
• Configure direct WOFF2 URLs for heading and body fonts and verify each loads correctly.
• Disable custom fonts and verify the existing Dawn font-picker selection is restored.
• Verify the password page uses the same custom font settings.
• Test on mobile and supported desktop browsers.
• Test accessibility and fallback rendering with a failed font URL.

Checklist

• Added PR summary for release notes
• Requested review from UX
• Created a ticket for the help.shopify.com documentation team about updates to theme settings. (Internal-only task)
• Followed theme code principles
• Linted with Theme Check
• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility

[HarshankPatel9038]

I have signed the CLA!