Add fat Ubuntu 26.04 base image with runit, Go, Node, Python toolchains

Single-RUN image built by build.sh on ubuntu:26.04: build-essential,
distro plus latest Go, nvm with Node LTS, corepack with yarn/pnpm cached,
wrangler, hugo extended, golangci-lint, pyenv with latest Python 3, pip
and virtualenv. runit services supervised under runsvinit as PID 1.
Docs, man pages, caches and non-English locales stripped.

Includes build logs for the 2026-11-05 release (amd64 and arm64).

Dockerfile

@@ -0,0 +1,30 @@
+# syntax=docker/dockerfile:1
+#
+# Fat base image: current Ubuntu LTS with Go, Node, Python, Hugo, and the
+# usual build tooling preinstalled, supervised by runit under runsvinit.
+# Builds for linux/amd64 and linux/arm64 from the same definition.
+# All the work happens in build.sh.
+
+FROM ubuntu:26.04
+
+# Pinned sources. Everything else (apt, Go, Node LTS, Python, Hugo,
+# golangci-lint, yarn, wrangler) resolves to its current release at build.
+ARG RUNSVINIT_COMMIT=b4b2c785308b1ce785b6155c7fe5f16879080193
+ARG NVM_GIT_TAG=v0.41.0
+ARG PYENV_GIT_TAG=v2.8.14
+
+ENV LANG=C.UTF-8 \
+    NVM_DIR=/usr/local/nvm \
+    NVM_SYMLINK_CURRENT=true \
+    COREPACK_HOME=/usr/local/corepack \
+    COREPACK_ENABLE_DOWNLOAD_PROMPT=0 \
+    COREPACK_ENABLE_AUTO_PIN=0 \
+    PYENV_ROOT=/usr/local/pyenv \
+    GOPATH=/root/go \
+    PATH=/usr/local/go/bin:/root/go/bin:/usr/local/nvm/current/bin:/usr/local/pyenv/shims:/usr/local/pyenv/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+
+COPY rootfs/ /
+ADD build.sh /tmp/build.sh
+RUN bash /tmp/build.sh
+
+CMD ["/usr/local/sbin/runsvinit"]