chore: remove Docker support entirely from this fork

Never used by this fork's own distribution (install.sh/x-ui.sh is the
only supported install path), AmneziaWG structurally can't run in the
Alpine-based image anyway, and Docker Hub publishing was failing on
every release for lack of configured credentials. Removed Dockerfile,
docker-compose.yml, DockerEntrypoint.sh, DockerInit.sh, .dockerignore,
and the docker.yml CI workflow; dropped the now-dead "Docker" README
subsection (all 7 languages), the "Docker image"/"Docker Compose"
options from the issue/PR templates, and corrected claude-bot.yml's
now-stale references to the deleted files, the never-actually-ours
ghcr.io/mhsanaei/3x-ui image, and (caught in passing) an already-stale
claim that Windows is a supported platform.

Left untouched: generic container-runtime adaptations that apply
regardless of image source (x-ui.sh's running-in-docker detection,
the virtual-interface-name filters, the DNS-over-container-network
note) and deploy/test/smoke-noninteractive.sh, which uses Docker only
as its own test sandbox, not as something this repo ships.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/pull_request_template.md

@@ -28,7 +28,6 @@ Link related issues here: "Closes #123", "Refs #456".
 - [ ] Statistics / traffic counters
 - [ ] Database / migrations
 - [ ] Install / upgrade script
-- [ ] Docker image
 - [ ] Multi-node (sub-nodes)
 - [ ] Telegram bot