fix: treat PID=1 as stale in PID file singleton check, fix govet shadow, add .gitattributes (#2642)

- pid: When a container stops and leaves behind a PID file with PID 1
  on a shared volume, the host's init process (PID 1) passes the
  isProcessRunning check, blocking new gateway starts. Treat recorded
  PID 1 as always stale in both WritePidFile and ReadPidFileWithCheck.
  Added unit tests covering the PID=1 container leftover scenario.

- isolation: Fix govet shadow warning on platform_windows.go line 105
  where := shadows the outer err variable. Changed to = assignment.

- gitattributes: Enforce LF line endings for shell scripts to prevent
  CRLF issues when checking out on Windows (breaks Docker entrypoint).

Co-authored-by: BeaconCat <BeaconCat@users.noreply.github.com>

docker/entrypoint.sh

@@ -12,4 +12,10 @@ if [ ! -d "${HOME}/.picoclaw/workspace" ] && [ ! -f "${HOME}/.picoclaw/config.js
     exit 0
 fi
 
+# Remove stale PID file from a previous container run.
+# After docker kill / OOM / crash the PID file may linger on the bind-mounted
+# volume and block the next gateway start (the recorded PID could collide with
+# an unrelated process inside the new container).
+rm -f "${HOME}/.picoclaw/.picoclaw.pid"
+
 exec picoclaw gateway "$@"