Feature: Pre-Export Form Validation & Digital Signatures

[YurMil]

Currently, form editing is basic. There is no verification of required fields, and users cannot sign documents locally.

Technical Proposal:

1. Add validation rules (e.g., email patterns, required fields) in validation.ts.
2. Prevent exporting or alert the user if any required forms are left empty.
3. Add a local signature pad using HTML5 Canvas inside the Inspector page, converting the signature to a transparent PNG and embedding it onto the selected page using pdf-lib's drawImage().

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