feat(podman): add optional Podman setup and documentation (#16273)

* feat(podman): add optional Podman setup and documentation

- Introduced `setup-podman.sh` for one-time host setup of OpenClaw in a rootless Podman environment, including user creation, image building, and launch script installation.
- Added `run-openclaw-podman.sh` for running the OpenClaw gateway as a Podman container.
- Created `openclaw.podman.env` for environment variable configuration.
- Updated documentation to include Podman installation instructions and a new dedicated Podman guide.
- Added a systemd Quadlet unit for managing the OpenClaw service as a user service.

* fix: harden Podman setup and docs (#16273) (thanks @DarwinsBuddy)

* style: format cli credentials

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Co-authored-by: Peter Steinberger <steipete@gmail.com>

docs/install/index.md

@@ -142,6 +142,9 @@ The **installer script** is the recommended way to install OpenClaw. It handles
   <Card title="Docker" href="/install/docker" icon="container">
     Containerized or headless deployments.
   </Card>
+  <Card title="Podman" href="/install/podman" icon="container">
+    Rootless container: run `setup-podman.sh` once, then the launch script.
+  </Card>
   <Card title="Nix" href="/install/nix" icon="snowflake">
     Declarative install via Nix.
   </Card>