feat: multi-image runners — go, node, docker, deploy, godot

Replace single fat image with purpose-built images per workflow type.
Each image is lean: base (Alpine+AWS+git) → go/node/deploy extend it.
docker image standalone (dind base). godot for future game builds.
build-all.sh builds base first, then all others in parallel.

images/docker/Dockerfile

@@ -0,0 +1,27 @@
+# tinqs/ci docker — Docker builds (platform image, bot image)
+# Used by: build (platform), deploy-bot
+# runs-on: docker
+# Based on docker:dind for Docker-in-Docker support.
+
+FROM docker:29-dind
+
+RUN apk add --no-cache \
+    bash git curl wget unzip tar \
+    ca-certificates openssh-client \
+    build-base s6 tzdata
+
+# AWS CLI
+RUN curl -fsSL https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip -o /tmp/awscli.zip && \
+    unzip -q /tmp/awscli.zip -d /tmp && \
+    /tmp/aws/install && \
+    rm -rf /tmp/awscli.zip /tmp/aws
+
+# Go (needed for platform Docker builds that compile inside container)
+ARG GO_VERSION=1.26.2
+RUN curl -fsSL "https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz" | tar -C /usr/local -xz
+ENV PATH="/usr/local/go/bin:/go/bin:${PATH}"
+ENV GOPATH="/go"
+
+RUN docker --version && aws --version && go version
+
+WORKDIR /workspace