fix: treat empty custom_fonts array as intent to remove default fonts

[Br1an67]

Problem

When custom_fonts is set to [] in theme.json, the user intends to manage fonts themselves (e.g., via @font-face in custom_css). However, the default Inter Google Font <link> tags are still injected because [] is falsy in Python, so the condition custom_theme.get("custom_fonts") evaluates to False.

This causes:

• Unnecessary network requests to fonts.googleapis.com
• Breakage in air-gapped/government environments where Google domains are blocked
• Privacy concerns (user IPs sent to Google)

Fix

• Check for key presence ("custom_fonts" in custom_theme) instead of truthiness
• Use if font is not None instead of if font so an empty string properly clears the default font tags via replace_between_tags

When custom_fonts is:

• absent → default Inter preserved (backward-compatible)
• [] → default Inter removed (user manages fonts)
• [{...}] → custom fonts replace Inter (existing behavior)

Fixes #2804

---

Summary by cubic

Stop injecting the default Inter font when theme.json sets custom_fonts to []. An empty array now removes the Inter links, reducing unwanted Google requests and supporting air-gapped environments. Fixes #2804.

• Bug Fixes
  • Check for key presence ("custom_fonts" in custom_theme) instead of truthiness so: absent → keep Inter, [] → remove Inter, [{...}] → use custom links.
  • Use if font is not None when replacing the FONT block so an empty string clears the tags.

^{Written for commit 0f69d69. Summary will update on new commits.}

[cubic-dev-ai]

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