Fix: improve performance by loading snippets only on manage screen

[rami-elementor]

The change in Manage_Menu.php makes snippetsList conditional.

Previously, every Manage Code Snippets page request localized the full result of get_snippets() into window.CODE_SNIPPETS_MANAGE, even when displaying the Community Cloud page or the Blueprints page (in Pro).

Now, it builds the common localized settings first, and only adds the full snippets payload when it's not a sub-page. As a result, it no longer loads the full result of snippets on subpages.

How does it affect different pages:

• /wp-admin/admin.php?page=snippets (no change)
• /wp-admin/admin.php?page=snippets&subpage=blueprints (optimized)
• /wp-admin/admin.php?page=snippets&subpage=cloud-community (optimized)

Performance benefits:

• Avoids get_snippets() on the Community Cloud subpage.
• Avoids a full SELECT * from the snippets table when the snippets cache is cold.
• Avoids hydrating every DB row into a Snippet object.
• Avoids per-snippet locked-status lookups via is_snippet_locked().
• Avoids mapping every Snippet through get_fields().
• Avoids printing the full snippets list into inline page JavaScript, which reduces HTML size, memory use, and parse/transfer cost.