[chore](trx-rs): add Podman act_runner CI deployment

Add container/: a rootless Podman + systemd (Quadlet) setup to run
per-project Gitea Actions runners on one host instead of VMs. Uses the
host executor with a purpose-built image that bakes in the Rust toolchain
and all build dependencies (opus, alsa, soapysdr, clang), so CI runs skip
the per-run install and cold soapysdr-sys build.

Includes the runner Containerfile, first-boot registration entrypoint,
act_runner config template, two Quadlet units (trx-rs + a second project),
and a README covering build, registration, the required host-executor
workflow tweak, and tuning.

Assisted-By: Claude Code (claude-opus-4)
Claude-Session: https://claude.ai/code/session_01NFpGtGTWUEYXLwZeZs2RAV
Signed-off-by: Stan Grams <sjg@haxx.space>

container/Containerfile

@@ -0,0 +1,59 @@
+# SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+#
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# Gitea Actions runner image for trx-rs CI (host-executor / "Pattern B").
+#
+# All build dependencies, the Rust toolchain, Node.js (for JS actions such as
+# actions/checkout and actions/cache) and the `reuse` tool are baked in, so CI
+# runs skip the per-run apt/rustup install cost. `sudo` is present so the
+# existing workflow's `sudo apt-get ...` / rustup steps remain valid — they
+# just become fast no-ops because everything is already installed.
+FROM docker.io/library/debian:bookworm-slim
+
+ARG ACT_RUNNER_VERSION=0.2.11
+ARG NODE_MAJOR=20
+
+ENV DEBIAN_FRONTEND=noninteractive \
+    RUSTUP_HOME=/opt/rustup \
+    CARGO_HOME=/opt/cargo \
+    PATH=/opt/cargo/bin:/usr/local/bin:/usr/bin:/bin
+
+# Base tooling + trx-rs build dependencies (mirrors .gitea/workflows/ci.yml).
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        ca-certificates curl xz-utils git sudo pipx \
+        build-essential pkg-config cmake clang libclang-dev \
+        libopus-dev libasound2-dev libsoapysdr-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+# Node.js (JS-based actions need node in PATH under the host executor).
+RUN curl -fsSL https://deb.nodesource.com/setup_${NODE_MAJOR}.x | bash - \
+    && apt-get install -y --no-install-recommends nodejs \
+    && rm -rf /var/lib/apt/lists/*
+
+# REUSE >= 3 (Debian's packaged reuse is too old for REUSE.toml).
+RUN PIPX_HOME=/opt/pipx PIPX_BIN_DIR=/usr/local/bin pipx install reuse
+
+# Rust stable with rustfmt + clippy, installed system-wide.
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
+        | sh -s -- -y --no-modify-path --profile minimal \
+          --component rustfmt --component clippy \
+    && chmod -R a+rwX "$CARGO_HOME" "$RUSTUP_HOME"
+
+# act_runner binary.
+RUN arch="$(dpkg --print-architecture)"; \
+    case "$arch" in amd64) rarch=amd64;; arm64) rarch=arm64;; *) echo "unsupported arch $arch" >&2; exit 1;; esac; \
+    curl -fsSL -o /usr/local/bin/act_runner \
+      "https://gitea.com/gitea/act_runner/releases/download/v${ACT_RUNNER_VERSION}/act_runner-${ACT_RUNNER_VERSION}-linux-${rarch}" \
+    && chmod +x /usr/local/bin/act_runner
+
+# Default config template (seeded into the /data volume on first boot).
+COPY config.yaml /etc/act_runner/config.yaml
+COPY entrypoint.sh /usr/local/bin/entrypoint.sh
+RUN chmod +x /usr/local/bin/entrypoint.sh
+
+# /data holds the .runner registration, cache and workflow workspaces.
+VOLUME /data
+WORKDIR /data
+
+ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]