Add smoke tests: PeerTube

[sij411]

Background

Part of the phase 3 interoperability smoke test rollout tracked in #682 .

PeerTube is a video-focused ActivityPub server. Its primary federation
unit is the channel, which is represented as a Group actor rather
than a Person. This makes it a good target for verifying Fedify's
handling of Group actors and Video objects.

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
• Note: PeerTube does not implement the Mastodon-compatible API.
  The provisioning script and any new scenarios must use the PeerTube
  REST API (/api/v1/*) directly

Test scenarios

The six baseline scenarios in orchestrator.ts do not apply here since
PeerTube does not implement the Mastodon-compatible API. The following
new scenarios are required:

• Fedify → PeerTube (Follow a channel): follow a PeerTube channel
  (Group actor) from the Fedify harness and verify Accept(Follow) is
  received
• PeerTube → Fedify (Announce(Video)): publish a video on PeerTube
  and verify the harness inbox receives an Announce(Video) activity

The Follow handler in federation.ts currently only accepts follows
from Person actors. It needs to be extended to also accept follows
where the target is a Group.

Acceptance criteria

• test/smoke/peertube/ is added with the required files:
  docker-compose.yml, Caddyfile.peertube, 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
• Both scenarios above pass reliably
• A GitHub Actions workflow (.github/workflows/smoke-peertube.yml) is
  added, triggered on pushes to main, next, and *.*-maintenance
  branches, and on workflow_dispatch