Add moqx client role

[gmarzot]

Summary

Adds a `client` role block to moqx's existing entry in `implementations.json`. Mirrors the pattern moxygen already uses.

moqx is currently registered relay-only, so it only appears in the relay column of the interop matrix. The moqx project already publishes an interop-client image (built alongside the relay image from the same tarball via multi-stage `FROM debian:bookworm AS builder`), so wiring it in here closes the loop.

Diff

```json
"moqx": {
...
"roles": {
"relay": { ... },
"client": {
"docker": {
"image": "ghcr.io/openmoq/moqx-interop-client:latest"
}
}
}
}
```

Image details

• Image: `ghcr.io/openmoq/moqx-interop-client:latest` (multi-arch: amd64 + arm64 manifest list)
• Also tagged: `:` per-build; `:main-latest` rolling; `:latest` back-compat alias on main pushes
• Base: `debian:bookworm-slim`
• Source: openmoq/moqx docker/Dockerfile.interop-client
• CI: auto-built + pushed on every push to `main` / `release/**` by ci-main.yml publish job

Runner conventions

The binary honors the runner's env-var conventions natively:

• `RELAY_URL` — target URL
• `TESTCASE` — per-test dispatch
• `TLS_DISABLE_VERIFY` — insecure mode for dev certs
• `VERBOSE` — GLOG verbosity

Output is TAP v14 to stdout. Same interface as moxygen's moq-interop-client since both link the same moxygen client library.

Test plan

• `generate-report.sh` renders moqx in both relay and client columns
• moqx-as-client × moxygen-as-relay passes setup + announce suites
• moqx-as-client × moq-dev-js-as-relay passes setup suite