feat: Add a "Content Edit Mode" for non-technical users

[maasanto]

Summary

Introduce a simplified edit mode in Frappe Builder that allows non-technical users to safely update text content and images on existing pages, without exposing layout, styling, or code-editing capabilities.

Problem

Frappe Builder is powerful but its full editor is overwhelming — and risky — for non-technical contributors (marketing, content editors, project owners). A small mistake (dragging a block, editing CSS, changing a class) can break the page layout. As a result, technical users end up handling routine content updates that should be self-service.

Proposed solution

A toggleable Content Edit Mode that restricts the editor to in-place content changes only:

Allowed in this mode:

• Edit text content (inline, WYSIWYG-style)
• Replace images (upload / pick from library)
• Edit links (URL + label)
• Edit button labels and links

Locked / hidden in this mode:

• Block structure (no add / delete / move / reorder)
• Layout and spacing controls
• CSS / class / style editing
• Script editor and code blocks
• Component creation and data sources
• Page settings

UX notes

• Toggle accessible from the top bar (e.g. "Content mode" / "Design mode")
• Visual cue: editable zones get a subtle outline on hover; everything else appears non-interactive
• Permission-based: a role (e.g. Builder Content Editor) could be restricted to this mode only, so non-technical users never see the full editor

Why this matters

• Empowers non-technical teams to maintain pages independently
• Reduces accidental layout breakage
• Makes Builder viable as a CMS-like tool in organizations with mixed technical skill levels

[federicocalvo]

Excelent feature!