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

cron/scheduler.py

@@ -341,26 +341,27 @@ def _deliver_result(job: dict, content: str, adapters=None, loop=None) -> Option
     from tools.send_message_tool import _send_to_platform
     from gateway.config import load_gateway_config, Platform
 
-    platform_map = {
-        "telegram": Platform.TELEGRAM,
-        "discord": Platform.DISCORD,
-        "slack": Platform.SLACK,
-        "whatsapp": Platform.WHATSAPP,
-        "signal": Platform.SIGNAL,
-        "matrix": Platform.MATRIX,
-        "mattermost": Platform.MATTERMOST,
-        "homeassistant": Platform.HOMEASSISTANT,
-        "dingtalk": Platform.DINGTALK,
-        "feishu": Platform.FEISHU,
-        "wecom": Platform.WECOM,
-        "wecom_callback": Platform.WECOM_CALLBACK,
-        "weixin": Platform.WEIXIN,
-        "email": Platform.EMAIL,
-        "sms": Platform.SMS,
-        "bluebubbles": Platform.BLUEBUBBLES,
-        "qqbot": Platform.QQBOT,
-        "yuanbao": Platform.YUANBAO,
-    }
+    # Accept any platform name — built-in names resolve to their enum
+    # member, plugin platform names create dynamic members via _missing_().
+    try:
+        platform = Platform(platform_name.lower())
+    except (ValueError, KeyError):
+        msg = f"unknown platform '{platform_name}'"
+        logger.warning("Job '%s': %s", job["id"], msg)
+        return msg
+
+    try:
+        config = load_gateway_config()
+    except Exception as e:
+        msg = f"failed to load gateway config: {e}"
+        logger.error("Job '%s': %s", job["id"], msg)
+        return msg
+
+    pconfig = config.platforms.get(platform)
+    if not pconfig or not pconfig.enabled:
+        msg = f"platform '{platform_name}' not configured/enabled"
+        logger.warning("Job '%s': %s", job["id"], msg)
+        return msg
 
     # Optionally wrap the content with a header/footer so the user knows this
     # is a cron delivery.  Wrapping is on by default; set cron.wrap_response: false