fix(followups): F2 - Python entry points report an unreadable env file in one line

A .mam.env that exists but cannot be read or decoded stopped the Python
entry points with an EnvFileError traceback, while the wrapper printed one
`ERROR:` line and exited 1 (PR #43 review claude S1). The mains that load the
env file - publish_event, registry, job_subscriber, cli, bench, heartbeat and
remote - now call mqtt_common.load_env_or_report(), which prints
`ERROR: <path>: cannot read (<exception type>)` and lets the main return 1.
No value or file content is printed. ensure_env_loaded() still raises: no
library function exits the process.

Test: every entry point, for a 000 file and an undecodable one, ends with
exactly that line and rc 1 and creates nothing (14 cases; all 14 fail at
0051fd6 with a traceback).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HCGpJXhSZasJLU38ksDghe

.agents/skills/lib_py/delegation/job_subscriber.py

@@ -587,7 +587,8 @@ def main(argv=None) -> int:
     parser.add_argument("-v", "--verbose", action="store_true")
     args = parser.parse_args(argv)
 
-    mqtt_common.ensure_env_loaded()
+    if not mqtt_common.load_env_or_report():
+        return 1
     mqtt_common.setup_logging(logging.DEBUG if args.verbose else logging.WARNING)
 
     try: