Write tests for resolveDockerHost (follow-up to #119)

[veksen]

Follow-up to #119, which added resolveDockerHost in src/remote/remote-controller.ts to auto-swap localhost for host.docker.internal when the docker-escaped host is reachable.

The function currently has no test coverage. We should add tests covering its branches.

Cases to cover

resolveDockerHost(db) should:

1. Non-localhost passthrough — return the input Connectable unchanged when db.isLocalhost() is false.
2. Same-hostname passthrough — when escapeDocker() returns a Connectable whose hostname matches the input (e.g., env.HOSTED=true, which makes escapeDocker() return this), return the original db without attempting to connect.
3. Docker host reachable — when host.docker.internal is reachable and SELECT 1 succeeds, return the escaped Connectable and log the resolution.
4. Docker host unreachable — when the probe throws, fall back to the original db and log the fallback.
5. Connection is always closed — the probe connection (pg.close()) is invoked in both success and failure paths (the finally branch).

Integration check

onFullSync should assign the resolved db to this.lastSourceDb (so a subsequent redump() uses the docker-escaped host) and pass it to remote.syncFrom.

Notes

• resolveDockerHost is a module-level function (not exported). Either export it for direct testing or exercise it through onFullSync + stubbed connectToSource / Connectable.
• Existing tests in src/remote/remote-controller.test.ts use PostgreSqlContainer and hit a real DB — the reachable-host case can follow that pattern; the unreachable case likely needs a mocked connectToSource.