support custom font url in branding config

[Coleton (Locrian24)]

Description

Companion to the portalv2 PR adding custom font support to branding: https://github.com/saasquatch/saasquatch/pull/new/font-uploading

When BrandingConfiguration.main.customFontUrl is set, inject an @font-face block (registered under brandFont as the family name) via a <style id="brandFontStylesheet"> tag instead of the Google Fonts <link>. Format is inferred from the URL extension:

• .woff2 → format("woff2")
• .woff → format("woff")
• .ttf → format("truetype")
• .otf → format("opentype")
• unknown extension → no format(...) (browser sniffs)

Both code paths (Google <link> and custom <style>) share the same DOM id so toggling modes replaces the element cleanly. customFontUrl is plumbed through parseBrandingConfig in global/styles.ts and the postMessage live-update path in global/global.ts for hot reloads from the editor.

Schema

main.customFontUrl?: string added to BrandingConfiguration in saasquatch.d.ts. Backward-compatible — existing configs without the field still take the Google Fonts path.

CSS variable

--sqm-primary-font continues to read from brandFont (the family name). Because the synthesized @font-face registers under that same name, no changes are needed in styles.ts's :root block.

How Has This Been Tested?

• Type-check passes on changed files. Pre-existing unrelated errors not introduced by this change.
• Manual (after portalv2 companion is wired): pick a Google font, confirm <link id="brandFontStylesheet"> is injected; switch to a custom URL/upload, confirm <style id="brandFontStylesheet"> with the right @font-face replaces it.
• Manual: confirm format inference for .woff2, .ttf, .otf.

Checklist:

• I have tested my changes locally
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings or errors in the console

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