story: Homepage, Contribute rename, and an "AI resources" page — final pass

[GigaHierz]

Part of #2266.

User story

As a first-time visitor (human or agent), I want the root of docs.celo.org to route me by what I'm trying to do, and to find in one place everything the docs offer to AI tools.

Context & evidence

At bdf40b37: the first page of the first tab is home/celo.mdx (title "Celo"), which already leads with agent cards (ERC-8004, x402, MPP, Celopedia) — 8 mentions of "agent". home/index.mdx ("What is Celo?") has 0. "Contribute to Celo" (docs.json:363) has 17 pages under contribute-to-celo/. What already ships for AI tools and is documented nowhere in one place: llms.txt (200, 39 KB), llms-full.txt (200, 1.5 MB), per-page .md export (200), the contextual menu (copy / view / mcp / chatgpt / claude / cursor / vscode), the hosted MCP endpoint at docs.celo.org/mcp (405 on GET — exists), the Celo MCP server page, Celopedia, the installable skills.

Scope — three small pieces, one final pass

1. Homepage. Make home/celo.mdx the real root landing page with jobs-to-be-done cards — build an agent that pays / build a Mini App / accept stablecoin payments / what is Celo / run a node — linking into the four tabs. Drop unexplained jargon from it ("Token Duality", "native transfer"). home/index.mdx becomes Learn's overview.
2. Contribute. Rename "Contribute to Celo" → "Contribute"; contribute-to-celo/* → contribute/*; catch-all redirect.
3. AI resources page under Build > Agents listing everything above, with one line on how to use each; add the assistant from story: Research and add an AI assistant to docs.celo.org (Mintlify-compatible, open source preferred) #2250 once it is live.

Acceptance criteria

• Root URL serves the card homepage
• Contribute renamed, paths shortened, redirects verified
• AI-resources page live, linked from the homepage and from use-docs-with-ai.mdx
• Final full-site npx mintlify broken-links + orphan check green
• Epic status table closed out

Non-goals

New agent content (#2263). The Startup Pathway link is not re-added (decided; it went with the Celo Camp removal in #2235).

Depends on / blocks

Depends on #2258, #2259, #2260. #2250 only for the assistant line — not a blocker.

Measured at: bdf40b37