Add scaffold-emdash-astro: extract roundtable template as reusable client scaffold

[stackbilt-admin]

Extract the roundtable repo's EmDash + Astro + CF Workers stack as a parameterized scaffold template.

What it gives agency clients:

• Visual CMS at /_emdash/admin (non-technical editing, no code required)
• Portable Text editor, image picker, draft/publish workflow, revisions
• D1 + R2 + KV bindings (CF-native, zero maintenance)
• Social distribution on publish (auto Bluesky/X)
• Edge performance (Astro 6 SSR on CF Workers, sub-20ms)

Extraction steps:

1. Copy seed/seed.json as parameterized template (swap collections per client)
2. Strip roundtable-specific content types, leave generic posts + pages
3. Genericize BaseLayout.astro (logo, nav, footer as config)
4. Make wrangler.jsonc bindings configurable via scaffold vars
5. Document customization guide (5 things to change per client)

Source: /mnt/c/Users/kover/Documents/roundtable
Template name: scaffold-emdash-astro

Why this matters: Closes the Duda competitive gap — agencies get a white-label site their clients can edit, running on edge infra at near-zero maintenance cost.