Admin index of all Mailchimp blocks/forms used across the site (locations, lists, quick actions)

[jeffpaul]

Is your enhancement related to a problem? Please describe.

What should be added or changed?

Provide an admin screen (e.g. under Mailchimp > Usage) that lists every location on the site where a Mailchimp form/block is present, similar to how taxonomy term usage or the 10up Block Catalog surfaces block locations.

Site owners frequently need to know "where Mailchimp forms are embedded" to update list targets, retire contest/temporary signups, or ensure brand/consent consistency. Today this requires manual hunting. A central index reduces operational overhead, improves compliance hygiene, and accelerates form maintenance.

The listing should include:

• Where: Post/Page/Template name + type + status, with quick links to Edit and View.
• Block details: Block type/variation (e.g., Mailchimp Form block), form ID/slug, and (if available) the Audience/List and tags/groups configured for that block instance.
• Context: Template/Template Part (for block themes), Reusable Block/Pattern references.
• Inline actions: Remove block from this location (with confirmation), or open the editor focused on the block.

Additionally the listing could include:

• Filters/Search: Filter by post type, status, template vs. content, list/audience, tag/group, and date updated.
• Export: CSV export of the table for audits.

QA considerations

• Verify detection across: posts, pages, CPTs, templates, template parts, reusable blocks, and patterns.
• Confirm accurate display of list/audience info when present in block attributes.
• Validate filters, search, pagination, and CSV export.
• Confirm permissions and nonces prevent unauthorized edits.
• Test on large content sets and with object caching enabled.

Designs

Acceptance Criteria

• New admin page lists all Mailchimp block instances across:

  • Posts, Pages, Custom Post Types
  • Site Editor Templates & Template Parts
  • Patterns/Reusable Blocks

• Each row shows: Title, Type, Status, Location (template/pattern if applicable), Audience/List (when available), Last Modified, and Actions (Edit, View).

• Search + filters (post type, status, audience/list, has tags/groups, location type).

• Works with both Classic and Block themes.

• Handles blocks in draft, scheduled, and trashed content gracefully (with status badges).

• Nonces and capability checks (edit_posts, edit_theme_options for templates) are respected.

• Performance: index build does not time out on large sites (support for pagination and background indexing).

• Optional CSV export.

Describe alternatives you've considered

Edge cases

• Multiple Mailchimp blocks on a single page show each row or group with a count and “expand” toggle.
• Blocks nested in patterns within templates display full path (Template → Pattern → Block).
• Classic Editor shortcodes (if any legacy shortcode exists) optional phase 2 discovery via content regex.
• Multisite: per-site index; future enhancement could add a network admin summary.

Out of scope (for v1)

• Editing block settings directly from the table (v1 links out to the editor).
• Automated audience/list reassignment in bulk (future enhancement).

Code of Conduct

• I agree to follow this project's Code of Conduct