Implement Context Menu Overrides w/ Font Family Fix

[PauloMFJ]

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After

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[gemini-code-assist]

Code Review

This pull request refactors typography styling by setting a global default font-family on the html element and removing redundant font-family declarations from typography mixins. It also overrides tldraw's default context menu and disables several unsupported actions (such as exporting, copying, and page movement). The feedback suggests explicitly setting form controls to inherit the font family, as they do not inherit from html by default, and using standard system fallbacks for serif and monospace fonts in tldraw instead of mapping them to the sans-serif "Google Sans" font.