v1.5.27 — Section template generation flow + section editor

What's Fixed

• Generation overlay not appearing — added position:fixed, z-index, and backdrop CSS to .bcg-generation-overlay
• Section template ignored on generation — JS startGeneration() now sends template_slug and section_template_id in the AJAX payload
• Flat copy generation ran for section campaigns — section campaigns now skip generate_campaign_copy() and generate_campaign_images(); content already AI-populated per section

What's Added

• Section editor in Edit Campaign page — shows per-section cards with editable AI fields (hero, text, banner, CTA) instead of flat headline/image/description fields for section-builder campaigns
• Save Section Content — saves all section field edits, re-renders email HTML server-side, and refreshes live preview
• Per-section Regenerate — bcg_regen_campaign_section AJAX handler regenerates AI content for one section by UUID