Add smoke tests: Akkoma/Pleroma

[sij411]

Background

Part of the phase 2 interoperability smoke test rollout tracked in #682.

Akkoma is an actively maintained fork of Pleroma and the two share the
same Elixir/OTP stack and API surface. Covering Akkoma effectively covers
the Pleroma lineage as a whole.

Docker image requirements

• Deployable via Docker Compose with no manual steps beyond configuration
• Exposes an HTTP endpoint reachable by the Caddy TLS proxy within the
  smoke Docker network
• Supports ActivityPub federation out of the box
• Allows programmatic account creation and API token issuance without
  requiring email verification
• Implements the Mastodon-compatible REST API (/api/v1/*)

Test scenarios

The six baseline scenarios in orchestrator.ts (Follow ↔, Create Note,
Reply, Unfollow ↔) should pass without modification since Akkoma/Pleroma
implement the Mastodon-compatible API. No new orchestrator scenarios are
required for this target.

Acceptance criteria (if it's akkoma)

• test/smoke/akkoma/ is added with the required files:
  docker-compose.yml, Caddyfile.akkoma, Caddyfile.fedify-harness,
  generate-certs.sh, provision.sh, and a server config file
• The provisioning script creates a test user, obtains an API token, and
  resolves the Fedify harness account
• All six baseline scenarios pass reliably
• A GitHub Actions workflow (.github/workflows/smoke-akkoma.yml) is
  added, triggered on pushes to main, next, and *.*-maintenance
  branches, and on workflow_dispatch