Add pay-x402 community extension with correct catalog-addition timestamps

[Copilot]

The review on #3741 flagged that the new pay-x402 catalog entry declared created_at/updated_at of 2026-07-25, while .github/workflows/add-community-extension.md requires a new entry's timestamps to be the actual catalog-addition date.

This branch is based on main, which does not yet contain the entry, so the #3741 addition is carried over here with the corrected timestamps.

Changes

• extensions/catalog.community.json — adds the pay-x402 entry with created_at/updated_at set to 2026-08-17T00:00:00Z, matching the suggested change. The top-level updated_at is already 2026-08-17T00:00:00Z on main, so it is unchanged.
• docs/community/extensions.md — adds the corresponding catalog table row in alphabetical position.

"pay-x402": {
  "name": "AgentPay x402 — Spend Controls for Spec Kit Agents",
  ...
  "created_at": "2026-08-17T00:00:00Z",
  "updated_at": "2026-08-17T00:00:00Z"
}

No CLI or extension code is touched; the change is catalog metadata plus the docs row it mirrors.

Opened on behalf of @mnriem by GitHub Copilot (autonomous).

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Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0 new
• Review effort level: Balanced