fix(gateway): guard yaml.safe_load and float() env var casts against crash

Two defensive fixes in gateway/run.py:

1. yaml.safe_load returning None on empty config files (line 12706):
   GatewayConfig.from_dict(data) crashes with AttributeError when the YAML
   file is empty because safe_load returns None. All 6 other yaml.safe_load
   call sites already use `or {}` — this one was missed.
   Impact: gateway fails to start with empty --config file.

2. float() on env vars without ValueError guard (lines 3951, 11757, 11805,
   11807): HERMES_AGENT_TIMEOUT, HERMES_AGENT_TIMEOUT_WARNING, and
   HERMES_AGENT_NOTIFY_INTERVAL are cast via float() directly from
   os.getenv(). A typo (e.g. "abc") raises ValueError and crashes the
   agent turn or gateway startup.
   Impact: single misconfigured env var crashes the entire gateway.

gateway/run.py

@@ -3948,7 +3948,10 @@ class GatewayRunner:
         # wall-clock age alone isn't sufficient.  Evict only when the agent
         # has been *idle* beyond the inactivity threshold (or when the agent
         # object has no activity tracker and wall-clock age is extreme).
-        _raw_stale_timeout = float(os.getenv("HERMES_AGENT_TIMEOUT", 1800))
+        try:
+            _raw_stale_timeout = float(os.getenv("HERMES_AGENT_TIMEOUT", 1800))
+        except (ValueError, TypeError):
+            _raw_stale_timeout = 1800.0
         _stale_ts = self._running_agents_ts.get(_quick_key, 0)
         if _quick_key in self._running_agents and _stale_ts:
             _stale_age = time.time() - _stale_ts
@@ -11755,7 +11758,10 @@ class GatewayRunner:
         # Config: agent.gateway_notify_interval in config.yaml, or
         # HERMES_AGENT_NOTIFY_INTERVAL env var.  Default 180s (3 min).
         # 0 = disable notifications.
-        _NOTIFY_INTERVAL_RAW = float(os.getenv("HERMES_AGENT_NOTIFY_INTERVAL", 180))
+        try:
+            _NOTIFY_INTERVAL_RAW = float(os.getenv("HERMES_AGENT_NOTIFY_INTERVAL", 180))
+        except (ValueError, TypeError):
+            _NOTIFY_INTERVAL_RAW = 180.0
         _NOTIFY_INTERVAL = _NOTIFY_INTERVAL_RAW if _NOTIFY_INTERVAL_RAW > 0 else None
         _notify_start = time.time()
 
@@ -11803,9 +11809,15 @@ class GatewayRunner:
             # Config: agent.gateway_timeout in config.yaml, or
             # HERMES_AGENT_TIMEOUT env var (env var takes precedence).
             # Default 1800s (30 min inactivity).  0 = unlimited.
-            _agent_timeout_raw = float(os.getenv("HERMES_AGENT_TIMEOUT", 1800))
+            try:
+                _agent_timeout_raw = float(os.getenv("HERMES_AGENT_TIMEOUT", 1800))
+            except (ValueError, TypeError):
+                _agent_timeout_raw = 1800.0
             _agent_timeout = _agent_timeout_raw if _agent_timeout_raw > 0 else None
-            _agent_warning_raw = float(os.getenv("HERMES_AGENT_TIMEOUT_WARNING", 900))
+            try:
+                _agent_warning_raw = float(os.getenv("HERMES_AGENT_TIMEOUT_WARNING", 900))
+            except (ValueError, TypeError):
+                _agent_warning_raw = 900.0
             _agent_warning = _agent_warning_raw if _agent_warning_raw > 0 else None
             _warning_fired = False
             _executor_task = asyncio.ensure_future(
@@ -12704,7 +12716,7 @@ def main():
     if args.config:
         import yaml
         with open(args.config, encoding="utf-8") as f:
-            data = yaml.safe_load(f)
+            data = yaml.safe_load(f) or {}
             config = GatewayConfig.from_dict(data)
     
     # Run the gateway - exit with code 1 if no platforms connected,