add Prism Network plugin

[akimstacks]

What this adds

Prism Network (plugin) — read-only MCP connector for a GPU compute network with per-second USDG pricing and a public onchain settlement receipt for every run.

Checklist

• This PR adds exactly ONE new file under content/ (plus assets for this entry, if any).
• It follows CONTRIBUTING.md — required fields + the golden rules (G1–G8).
• npm run validate passes locally (schema, slug, vocabularies).
• slug is kebab-case and exactly matches the filename.
• I ran / used this myself end to end — it works today.
• Every URL in the frontmatter resolves to real, relevant content.
• The prompt body is the real, complete prompt — not a summary or a teaser.
• The entry body is plain markdown — no raw HTML.
• I did NOT set verified_at or status: live — status is proposed.
• This is not an ad: every tool on the connector is read-only and free; nothing in the entry can spend or upsell.
• This is our own work (author = Prism Network).
• I license this contribution under CC BY 4.0.

Where it came from

Our own connector: https://prismnetwork.tech/api/mcp, docs at https://docs.prismnetwork.tech/.