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

hermes_cli/platforms.py

@@ -44,6 +44,40 @@ PLATFORMS: OrderedDict[str, PlatformInfo] = OrderedDict([
 
 
 def platform_label(key: str, default: str = "") -> str:
-    """Return the display label for a platform key, or *default*."""
+    """Return the display label for a platform key, or *default*.
+
+    Checks the static PLATFORMS dict first, then the plugin platform
+    registry for dynamically registered platforms.
+    """
     info = PLATFORMS.get(key)
-    return info.label if info is not None else default
+    if info is not None:
+        return info.label
+    # Check plugin registry
+    try:
+        from gateway.platform_registry import platform_registry
+        entry = platform_registry.get(key)
+        if entry:
+            return f"{entry.emoji}  {entry.label}" if entry.emoji else entry.label
+    except Exception:
+        pass
+    return default
+
+
+def get_all_platforms() -> "OrderedDict[str, PlatformInfo]":
+    """Return PLATFORMS merged with any plugin-registered platforms.
+
+    Plugin platforms are appended after builtins.  This is the function
+    that tools_config and skills_config should use for platform menus.
+    """
+    merged = OrderedDict(PLATFORMS)
+    try:
+        from gateway.platform_registry import platform_registry
+        for entry in platform_registry.plugin_entries():
+            if entry.name not in merged:
+                merged[entry.name] = PlatformInfo(
+                    label=f"{entry.emoji}  {entry.label}" if entry.emoji else entry.label,
+                    default_toolset=f"hermes-{entry.name}",
+                )
+    except Exception:
+        pass
+    return merged