[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/README.md

@@ -0,0 +1,118 @@
+<!--
+SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+SPDX-License-Identifier: GPL-2.0-or-later
+-->
+
+# Podman-based Gitea Actions runners
+
+Run two independent Gitea Actions runners on one host as rootless Podman
+containers managed by systemd (Quadlet) — one per project — instead of two
+VMs. Uses the **host executor**: workflow steps run directly inside a
+purpose-built runner image that already has the Rust toolchain and all build
+dependencies baked in, so CI runs skip the per-run install cost and no
+Docker/Podman socket is needed.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `Containerfile` | Runner image: Debian + build deps + clang + Rust + Node + `reuse` + `act_runner`. |
+| `entrypoint.sh` | Registers on first boot (if needed), then runs the daemon. |
+| `config.yaml` | act_runner config template (seeded into each runner's volume). |
+| `trx-rs-runner.container` | Quadlet unit for the trx-rs runner. |
+| `project2-runner.container` | Quadlet unit for the second project's runner. |
+
+## Prerequisites (once per host)
+
+Rootless Podman with cgroups v2 (default on modern distros). As the unprivileged
+user that will own the runners:
+
+```bash
+# Survive logout / start on boot without an interactive session.
+loginctl enable-linger "$USER"
+```
+
+No `podman.socket` is required for the host executor.
+
+## 1. Build the image
+
+```bash
+cd container
+podman build -t trx-rs-ci:latest .
+```
+
+## 2. Get a registration token
+
+For **each** repo: *Settings → Actions → Runners → Create new Runner* and copy
+the token. (Org- or instance-level tokens work too if you prefer wider scope.)
+
+## 3. Install and start the runners
+
+```bash
+mkdir -p ~/.config/containers/systemd
+cp trx-rs-runner.container project2-runner.container ~/.config/containers/systemd/
+
+# Paste each repo's token for the FIRST boot only:
+#   Environment=GITEA_RUNNER_REGISTRATION_TOKEN=xxxx…
+$EDITOR ~/.config/containers/systemd/trx-rs-runner.container
+$EDITOR ~/.config/containers/systemd/project2-runner.container
+
+systemctl --user daemon-reload
+systemctl --user start trx-rs-runner
+systemctl --user start project2-runner
+
+systemctl --user status trx-rs-runner
+podman logs -f gitea-runner-trx-rs
+```
+
+Once each runner shows **online** in the repo's runner list, blank out the
+`GITEA_RUNNER_REGISTRATION_TOKEN` line again (the registration is persisted in
+the `…-data` volume) and `systemctl --user daemon-reload`.
+
+## Required workflow change: the `reuse` job
+
+The host executor runs steps directly in the container and therefore **cannot
+run Docker-based actions**. The current `reuse` job uses `fsfe/reuse-action@v5`,
+which is a Docker action. `reuse` is baked into the image, so replace that job
+with a plain command:
+
+```yaml
+  reuse:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: REUSE compliance
+        run: reuse lint
+```
+
+The `lint` and `test` jobs need no changes: their `sudo apt-get …` and rustup
+steps still run, but become fast no-ops because the image already has those
+packages and the toolchain. (`sudo` is included in the image for exactly this
+reason.)
+
+> If you would rather keep Docker-based actions and per-run images, use the
+> **Docker executor** instead: drop the `:host` suffix from the label in
+> `config.yaml`, enable `systemctl --user --now enable podman.socket`, mount it
+> into the container, and set `container.docker_host` to the socket path. That
+> trades the baked-in speed for stronger per-job isolation.
+
+## Tuning
+
+- **`capacity`** (in `config.yaml`) — concurrent jobs per runner. Rust builds
+  are heavy; 1–2 is sensible when two runners share a host.
+- **`PodmanArgs=--cpus/--memory`** (in each `.container`) — hard resource caps
+  so one project cannot starve the other.
+- **SELinux** — the `:Z` volume flag is already set; keep it if SELinux is
+  enforcing.
+
+## Committing these files
+
+If you add this directory to a REUSE-checked repo, register the markdown in
+`REUSE.toml` (the other files carry inline SPDX headers):
+
+```toml
+[[annotations]]
+path = ["container/**"]
+SPDX-FileCopyrightText = "2026 Stan Grams <sjg@haxx.space>"
+SPDX-License-Identifier = "GPL-2.0-or-later"
+```