Add Tugboat preview environment support #2569

Summary

Vortex offers PR/preview environments through Lagoon, but not every client is on Lagoon. Tugboat is a common preview-environment provider, and supporting it would give teams a second option for per-PR previews without committing to a particular hosting stack.

We should add Tugboat support to the template.

(Related: there was an earlier exploration of this in #555, closed back in 2022. The architecture has moved on a long way since then, so this is a fresh take scoped to current Vortex rather than a reopen.)

What we'd add

• A .tugboat/config.yml for the Vortex service stack: web server, PHP, database, and the optional services Vortex ships (Redis/Valkey, Solr, ClamAV).
• A settings.tugboat.php environment include that wires up DB credentials, trusted host patterns, hash salt, mail capture, and the environment indicator, consistent with how the other provider includes work.
• A way to seed the preview database from the project's configured DB source, so previews come up with real content.

Why it's worth doing

• A second preview-environment provider widens the set of hosting setups Vortex fits into.
• Preview environments are one of the highest-value bits of the developer workflow, and right now they're effectively Lagoon-only.

Scope notes

• Ideally the Tugboat config is generated or derived from the existing service definitions rather than maintained as a separate hand-written stack, to avoid drift as the Docker setup evolves.
• Should be an opt-in service selectable at install time, like the other optional integrations.

Acceptance criteria

• A Tugboat config builds a working preview environment for the default Vortex stack.
• The optional services (Redis, Solr, ClamAV) are handled when enabled.
• Previews come up provisioned with content from the configured DB source.
• Tugboat is an opt-in choice in the installer.