#9992: Docker: Fixed port mapping so ports publish when not stated

On Windows (and when compose runs without the setup script’s env or a complete `.env`), the gateway and bridge ports weren’t published. Using fixed `18789:18789` and `18790:18790` ensures they’re always mapped. Also added a “Can’t reach the dashboard” troubleshooting section to the Docker install docs. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates the Docker Compose setup to always publish the gateway and bridge ports by hard-coding host mappings to `18789:18789` and `18790:18790`, addressing cases where `.env` is missing/empty (notably on Windows). It also adds a new “Can’t reach the dashboard” troubleshooting section to the Docker install docs, with steps to verify the container is running, confirm the URL, validate port mapping, run a health check, and re-run onboarding. <h3>Confidence Score: 4/5</h3> - Mostly safe to merge, but docs/config semantics need alignment. - Changes are small and localized, but hard-coding ports changes expected behavior (env-based overrides) and the new docs currently describe an override mechanism that no longer works with the compose file as changed. - docker-compose.yml, docs/install/docker.md <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->