v2.6.0: theme regions, gt-page-block rename + migration, REST API, library panel

What's Changed

Theme building

• Library blocks can be assigned to theme regions — header, hero, before/after content, sidebar, footer, 404 — and rendered by any theme via gt_pb_region( 'header' ) / gt_pb_has_region(). A blank hybrid theme can be little more than region calls.
• Hook positions now actually render: wp_head, wp_body_open, wp_footer, loop_start/loop_end, get_header/footer/sidebar, and before/after the content — priority-ordered.

Block rename + migration

• The block is now gt-page-block/page-block (category: Page Blocks). The legacy marketers-delight/page-block stays registered (hidden from the inserter) so existing content keeps rendering, with a one-click transform to the new block.
• Migration tool: Settings → Tools → Migrate blocks (with dry run), or WP-CLI wp gt-pb migrate-blocks [--dry-run] — rewrites stored content without touching post modified dates.

REST API (pbb/v1)

• GET/POST /blocks, GET/PUT/DELETE /blocks/<id> (trash or ?force=true), POST /blocks/<id>/duplicate, GET /blocks/<id>/render — search, status filtering, pagination, and status-count headers. Read = edit_posts, write = manage_options.

Library admin panel

• New card-grid library with lazy live-preview thumbnails, search, status filter tabs, duplicate / trash / restore / delete-forever, copy-shortcode, and position chips. Classic list table remains at ?view=list.

Block editor

• Preview-first Page Block: rendered live preview (auto-sizing iframe with theme styles) by default; Preview/Code toggles in the block toolbar.
• Responsive viewport presets (desktop / 768px / 390px) + dark-scheme preview toggle.
• Collapsible live preview pane under the CodeMirror editor — server-rendered when PHP/wpautop is enabled.
• Copy button, Save to library, and a Browse library modal to insert saved blocks.

Full Changelog: v2.4.0...v2.6.0