Add city-only Provider Listings meta box with JSON-safe persistence

[Copilot]

community posts currently store provider_listings as a raw JSON string consumed by WPGraphQL, but editors had no admin UI to maintain it. This change adds an editor-facing meta box for city pages and preserves JSON escape integrity by writing via $wpdb instead of metadata APIs that unslash values.

• Admin UI (city-level only)

  • Registers a Provider Listings meta box on community edit screens only when listing_type = city.
  • Places the box in normal context with high priority.
  • Renders a 20-row JSON textarea prefilled with pretty-printed JSON (JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE) when parseable.

• Editor feedback in-box

  • Displays live byte count and provider count.
  • Adds inline client-side JSON validation on blur/change/input:
    • invalid JSON → red border + inline error
    • valid JSON → clears error state

• Save path and data integrity

  • Adds nonce generation/verification (wp_create_nonce / wp_verify_nonce) and edit_posts capability gating.
  • Validates submitted JSON with json_decode; invalid payloads are not persisted and surface an admin notice:
    • Provider Listings not saved: invalid JSON.
  • Persists valid JSON through direct SQL update to wp_postmeta using $wpdb->update() (with insert fallback when row is missing), avoiding update_post_meta() unslash corruption.

• Plugin wiring

  • Introduces ProviderListingsMetaBox admin component and registers it in plugin bootstrap.

$updated = $wpdb->update(
    $wpdb->postmeta,
    [ 'meta_value' => $json_string ],
    [ 'post_id' => $post_id, 'meta_key' => 'provider_listings' ],
    [ '%s' ],
    [ '%d', '%s' ]
);

[sanruiz]

LGTM

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Invalidate post-meta cache after direct writes

When a persistent object cache is enabled, this direct $wpdb->update() leaves WordPress' post_meta cache stale. The method already calls get_post_meta() for listing_type, which primes the meta cache for the whole post before this write, so later get_post_meta( $post_id, 'provider_listings', true ) calls (including WPGraphQL consumers) can keep returning the old JSON even though the database row changed. Please clear or update the post meta cache after both the update and insert paths while preserving the direct SQL write.

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