fix(watchdog): eliminate SIGPIPE+pipefail phantom failures in health checks

echo "$list" | grep -q under set -o pipefail exits 141 whenever grep
matches before echo finishes writing, so healthy browsers were reported
'CDP up but no page target' and killed every 2 min fleet-wide (load 19+).
Use [[ == *glob* ]] (no pipe, no race) for the page/muse.ai stages, and
grep -c (reads to EOF, never early-exits) for the netns check.

bin/chromebox-watchdog.sh

@@ -64,9 +64,9 @@ healthy() {
   local list
   list="$(cdp_list)" \
     || { HEALTH_FAIL_REASON="CDP unreachable on :$CDP_PORT"; return 1; }
-  echo "$list" | grep -q '"type": "page"' \
+  [[ "$list" == *'"type": "page"'* ]] \
     || { HEALTH_FAIL_REASON="CDP up but no page target in list"; return 1; }
-  echo "$list" | grep -E -q '"url": "https://muse\.ai' \
+  [[ "$list" == *'"url": "https://muse.ai'* ]] \
     || { HEALTH_FAIL_REASON="CDP up but not on muse.ai"; return 1; }
   warp_egress_healthy || return 1
   return 0