gitea-actions: run CI jobs in rootless-podman containers

Switch the act_runners from :host execution to docker:// images backed by
a rootless podman socket under the gitea-runner user, so each job runs in
its own ephemeral container with per-job Go caches. This eliminates the
cross-repo GOMODCACHE/go-build poisoning that forced the debyl runner to
capacity:1.

- deps.yml: enable the rootless --user podman.socket, ensure subuid/subgid,
  register gitea_runner_uid; drop the rootful system socket override,
  podman-docker and host golang
- images.yml + Containerfile.ci/.espidf: build localhost/gitea-ci and
  localhost/gitea-ci-espidf into the runner's rootless image store
- config.yaml.j2: docker:// labels (per-runner overridable), docker_host
  -> rootless socket, force_pull false
- act_runner.service.j2: XDG_RUNTIME_DIR + DOCKER_HOST -> user socket
- defaults: uniform capacity:4 (drop the debyl capacity:1 workaround);
  esp_idf_version now tags the espressif/idf-based image
- main.yml: import images.yml, drop the host esp-idf install (firmware jobs
  use the espressif/idf job container instead)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ansible/roles/gitea-actions/templates/Containerfile.ci

@@ -0,0 +1,24 @@
+# Default Gitea Actions job image (managed by ansible: roles/gitea-actions).
+# Covers Go/web/node jobs plus `docker build` (talks to the mounted rootless
+# podman socket). Go toolchains are provided per-job by actions/setup-go.
+FROM node:20-bookworm-slim
+
+ARG DOCKER_CLI_VERSION=27.3.1
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        ca-certificates curl git openssh-client make build-essential \
+        python3 python3-pip jq unzip \
+    && rm -rf /var/lib/apt/lists/*
+
+# Static docker client (no daemon) for jobs that run `docker build` against the
+# mounted podman socket (/var/run/docker.sock).
+RUN curl -fsSL "https://download.docker.com/linux/static/stable/x86_64/docker-${DOCKER_CLI_VERSION}.tgz" \
+        | tar -xz -C /tmp \
+    && install -m0755 /tmp/docker/docker /usr/local/bin/docker \
+    && rm -rf /tmp/docker
+
+# AWS CLI v2 — several workflows upload artifacts / deploy Lambda.
+RUN curl -fsSL "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o /tmp/awscliv2.zip \
+    && unzip -q /tmp/awscliv2.zip -d /tmp \
+    && /tmp/aws/install \
+    && rm -rf /tmp/aws /tmp/awscliv2.zip