Add Font manager

Feature Description

Add font management for document fields so users can upload custom fonts and apply them to text-like fields across document editing, signing, preview, and final PDF generation.

The feature supports personal, team, and organisation font libraries, allowing different scopes to manage and reuse their own uploaded font assets.

Use Case

Teams often need signed documents to match their brand or template requirements. Without custom font support, text fields, generated PDFs, and signing previews can render with default fonts that do not match the source document or organisation style guide.

This is especially useful for:

• Branded contracts and agreements.
• Templates shared across a team or organisation.
• Documents where inserted field text must visually match the surrounding PDF.
• Signing flows where preview, signing, partial download, and final sealed PDF output should stay consistent.

Proposed Solution

Implement a font manager that allows users to upload supported font files, manage them by ownership scope, and select those fonts when configuring document fields.

The implementation should include:

• Personal, team, and organisation font libraries.
• Upload validation for supported font files and file size limits.
• Display names for uploaded fonts.
• Font access checks based on the current user, team, organisation, or recipient signing token.
• Font selection in text-like field settings.
• Bold and italic styling controls for supported fields.
• Rendering support in editor previews, signing views, partial downloads, and final signed PDF output.
• Dynamic @font-face loading for uploaded fonts.
• PDF embedding support so downloaded and sealed PDFs preserve selected typography.

Alternatives (optional)

A simpler alternative would be to only allow a fixed set of built-in fonts. That would avoid upload and access-control complexity, but would not solve branded document or organisation-specific typography needs.

Additional Context

Implementation PR: https://github.com/documenso/documenso/pull/2990

Associated branch: dadastory:feat/font-management

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