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/handlers/main.yml

@@ -6,16 +6,3 @@
     state: restarted
     daemon_reload: true
   loop: "{{ gitea_runners }}"
-
-- name: restart podman socket
-  become: true
-  ansible.builtin.systemd:
-    name: podman.socket
-    state: restarted
-    daemon_reload: true
-
-- name: restore esp-idf selinux context
-  become: true
-  ansible.builtin.command:
-    cmd: restorecon -R {{ esp_idf_path }}
-  changed_when: true