fix: sed escaping and UID mismatch in Podman Quadlet setup (#26414)

* fix: sed escaping and UID mismatch in Podman Quadlet setup

Fix two bugs in the Podman/Quadlet installation path:

1. setup-podman.sh line 227: Remove `/` from sed escape character class.
   The sed substitution uses `|` as delimiter, so `/` doesn't need
   escaping. Including it causes paths like `/home/openclaw` to become
   `\/home\/openclaw`, which Podman rejects as invalid volume names.

2. openclaw.container.in: Add `User=%U:%G` after `UserNS=keep-id`.
   The Dockerfile sets `USER node` (UID 1000), but the `openclaw` system
   user created by setup-podman.sh may get a different UID (e.g., 1001).
   Without `User=%U:%G`, the container process runs as UID 1000 and
   cannot read config files owned by the openclaw user.

Closes #26400

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* scripts: extract quadlet sed replacement escaping helper

* podman: document quadlet user mapping rationale

* scripts: correct sed replacement escaping for pipe delimiter

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Vincent Koc <vincentkoc@ieee.org>

scripts/podman/openclaw.container.in

@@ -9,6 +9,8 @@ Description=OpenClaw gateway (rootless Podman)
 Image=openclaw:local
 ContainerName=openclaw
 UserNS=keep-id
+# Keep container UID/GID aligned with the invoking user so mounted config is readable.
+User=%U:%G
 Volume={{OPENCLAW_HOME}}/.openclaw:/home/node/.openclaw
 EnvironmentFile={{OPENCLAW_HOME}}/.openclaw/.env
 Environment=HOME=/home/node