fix(zulip-monitor): stream alert body now carries real content, plain & params, WARN on delivery failure

The #agent-hub / zulip-health stream post in notify() encoded content with
python quote(str()) (always empty), so every stream alert posted empty
content and Zulip rejected it silently behind '|| true'. The merged body
also used backslash-escaped ampersands inside double quotes, which curl
transmits literally (type=stream\ -> Zulip 400 'Invalid type').

Stream post now percent-encodes the real message text by piping it through
the encoder (locale-proof: quote_from_bytes on stdin.buffer), uses plain &
separators, and on failure appends one WARN line to the monitor log with
the curl exit status instead of silently swallowing it. Delivery failure
stays non-fatal and unretried. DM path, probes, alive rule, exit codes and
log format unchanged.

scripts/zulip-monitor.sh

@@ -29,8 +29,9 @@ notify() {
   local stream_content="${severity} Zulip Monitor: ${msg}"
   curl -sf -X POST "${ZULIP_SITE}/api/v1/messages" \
     -u "${ZULIP_EMAIL}:${ZULIP_KEY}" \
-    -d "type=stream\&to=%5B7%5D\&topic=zulip-health\&content=$(python3 -c "import urllib.parse; print(urllib.parse.quote(str()))")" \
-    > /dev/null 2>&1 || true
+    -d "type=stream&to=%5B7%5D&topic=zulip-health&content=$(printf '%s' "${stream_content}" | python3 -c "import sys,urllib.parse; print(urllib.parse.quote_from_bytes(sys.stdin.buffer.read()))")" \
+    > /dev/null 2>&1 \
+    || echo "  WARN: stream alert to #agent-hub (zulip-health) delivery failed (curl exit $?)" >> "$LOG"
 }
 
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