feat: complete plugin platform parity — all 12 integration points

Extends the platform plugin interface from Phase 1 to cover every
touchpoint where built-in platforms have hardcoded behavior.

- allowed_users_env / allow_all_env: per-platform auth env vars
- max_message_length: smart-chunking for send_message tool
- pii_safe: session PII redaction flag
- emoji: CLI/gateway display
- allow_update_command: /update access control

send_message tool (tools/send_message_tool.py):
- Replaced hardcoded platform_map dict with Platform() call
- Added _send_via_adapter() for plugin platforms — routes through
  live gateway adapter when available
- Registry-aware max message length for smart chunking

Cron delivery (cron/scheduler.py):
- Replaced hardcoded 15-entry platform_map with Platform() call
- Plugin platforms now work as cron delivery targets

User authorization (gateway/run.py _is_user_authorized):
- Registry fallback: checks PlatformEntry.allowed_users_env and
  allow_all_env when platform not in hardcoded maps
- Plugin platforms get per-platform auth support

_UPDATE_ALLOWED_PLATFORMS: checks registry allow_update_command flag
Channel directory: includes plugin platforms in session enumeration
Orphaned config warning: descriptive message when plugin platform is
  in config but no plugin registered it
Gateway weakref: _gateway_runner_ref for cross-module adapter access

hermes status: shows plugin platforms with (plugin) tag
hermes gateway setup: plugin platforms appear in menu with setup hints
hermes_cli/platforms.py: get_all_platforms() merges with registry,
  platform_label() falls back to registry for plugin names

- 8 new tests (extended fields, cron resolution, platforms merge)
- Updated 3 tests for new Platform() based resolution
- 2829 passed, 24 pre-existing failures, zero new failures

gateway/run.py

@@ -782,6 +782,13 @@ def _format_gateway_process_notification(evt: dict) -> "str | None":
     return None
 
 
+# Module-level weak reference to the active GatewayRunner instance.
+# Used by tools (e.g. send_message) that need to route through a live
+# adapter for plugin platforms.  Set in GatewayRunner.__init__().
+import weakref as _weakref
+_gateway_runner_ref: _weakref.ref = lambda: None
+
+
 class GatewayRunner:
     """
     Main gateway controller.
@@ -806,9 +813,11 @@ class GatewayRunner:
     _session_reasoning_overrides: Dict[str, Dict[str, Any]] = {}
 
     def __init__(self, config: Optional[GatewayConfig] = None):
+        global _gateway_runner_ref
         self.config = config or load_gateway_config()
         self.adapters: Dict[Platform, BasePlatformAdapter] = {}
         self._warn_if_docker_media_delivery_is_risky()
+        _gateway_runner_ref = _weakref.ref(self)
 
         # Load ephemeral config from config.yaml / env vars.
         # Both are injected at API-call time only and never persisted.
@@ -2483,7 +2492,17 @@ class GatewayRunner:
             
             adapter = self._create_adapter(platform, platform_config)
             if not adapter:
-                logger.warning("No adapter available for %s", platform.value)
+                # Distinguish between missing builtin deps and missing plugin
+                _pval = platform.value
+                _builtin_names = {m.value for m in Platform.__members__.values()}
+                if _pval not in _builtin_names:
+                    logger.warning(
+                        "No adapter for '%s' — is the plugin installed? "
+                        "(platform is enabled in config.yaml but no plugin registered it)",
+                        _pval,
+                    )
+                else:
+                    logger.warning("No adapter available for %s", _pval)
                 continue
             
             # Set up message + fatal error handlers
@@ -3462,6 +3481,19 @@ class GatewayRunner:
             Platform.YUANBAO: "YUANBAO_ALLOW_ALL_USERS",
         }
 
+        # Plugin platforms: check the registry for auth env var names
+        if source.platform not in platform_env_map:
+            try:
+                from gateway.platform_registry import platform_registry
+                entry = platform_registry.get(source.platform.value)
+                if entry:
+                    if entry.allowed_users_env:
+                        platform_env_map[source.platform] = entry.allowed_users_env
+                    if entry.allow_all_env:
+                        platform_allow_all_map[source.platform] = entry.allow_all_env
+            except Exception:
+                pass
+
         # Per-platform allow-all flag (e.g., DISCORD_ALLOW_ALL_USERS=true)
         platform_allow_all_var = platform_allow_all_map.get(source.platform, "")
         if platform_allow_all_var and os.getenv(platform_allow_all_var, "").lower() in ("true", "1", "yes"):
@@ -8761,8 +8793,16 @@ class GatewayRunner:
 
         # Block non-messaging platforms (API server, webhooks, ACP)
         platform = event.source.platform
-        if platform not in self._UPDATE_ALLOWED_PLATFORMS:
-            return "✗ /update is only available from messaging platforms. Run `hermes update` from the terminal."
+        _allowed = self._UPDATE_ALLOWED_PLATFORMS
+        # Plugin platforms with allow_update_command=True are also allowed
+        if platform not in _allowed:
+            try:
+                from gateway.platform_registry import platform_registry
+                entry = platform_registry.get(platform.value)
+                if not entry or not entry.allow_update_command:
+                    return "✗ /update is only available from messaging platforms. Run `hermes update` from the terminal."
+            except Exception:
+                return "✗ /update is only available from messaging platforms. Run `hermes update` from the terminal."
 
         if is_managed():
             return f"✗ {format_managed_message('update Hermes Agent')}"