feat: embed forms on external websites

[harshtandiya]

Overview

Allow published Forms Pro forms to be embedded directly into external (non-Frappe) websites.

Proposed Approaches

• iframe embed — simple copy-paste snippet, isolated rendering
• Script embed — JS snippet that mounts the form inline, better UX, supports theming

Requirements

• CORS configuration for embed domains
• Embed snippet available from the form share/publish screen
• Submissions from embedded forms attributed correctly
• Handle auth for public vs gated forms