Replace the old "Contribute an Activity Guide" page with a new "What are Activity Guides?" page, including overview and draft contribution guidance. Update the Activity Guide Library page to add a dedicated submission section and licensing note so contribution info is surfaced there as well.

Reworks Activity Guide zines to load from file-backed cards sorted by required `order` frontmatter, with explicit placeholder entries (`placeholder: true`) that render “Guide wanted” cards but do not generate detail pages. Published zines now support optional covers, optional license blocks, local or external PDF downloads, and required human-readable `file_size` metadata.

Introduces reusable `BackButton` and `ZineDownloads` components, updates grid/detail rendering and styles for cover fallbacks, adds new zine/placeholder content entries (including Zine Making Kit), and updates schema/validation logic by removing fixed topic-slot uniqueness in favor of id/identity checks. Tests and docs were expanded to cover ordering, placeholder behavior, external downloads, and emitted asset expectations.

Placeholder Activity Guide cards now show a “Submit a zine” button that opens the Discourse new-topic form with the topic prefilled in both the title and submission template body. This replaces the old “Guide wanted” placeholder text, updates card styling/layout, and refreshes Organizer Kit and zine documentation copy to match. Tests were updated to assert the new button text and prefilled URL behavior.

Updates the Organizer Kit copy and navigation labels to use "Zine Library" instead of "Activity Guide Library," and reorders the two related docs so the overview page comes first. Also refreshes the submission template text to match the new naming.

Rename "resources" to "event resource", add "additional guides", and reorder sections

Add support for using .env for local dev carto.com API key. Introduces `src/lib/carto.ts` with a `cartoTileUrl()` helper that appends `PUBLIC_CARTO_API_KEY` (`import.meta.env.DEV`). MapView and NodePanel now use this helper for all CARTO basemap layers, so local development can use keyed tile requests without affecting production URLs. AGENTS.md was updated to document the new helper and the local `.env` behavior.

Only render the docs page table of contents when there is more than one h2 heading. This avoids showing an unnecessary “On this page” block on pages with a single section.