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/gateway.py

@@ -3779,35 +3779,61 @@ def gateway_setup():
         print()
         print_header("Messaging Platforms")
 
+        # Build menu from built-in platforms + plugin platforms
+        _plugin_entries = []
+        try:
+            from gateway.platform_registry import platform_registry
+            _plugin_entries = platform_registry.plugin_entries()
+        except Exception:
+            pass
+
         menu_items = []
         for plat in _PLATFORMS:
             status = _platform_status(plat)
             menu_items.append(f"{plat['label']}  ({status})")
+        for pentry in _plugin_entries:
+            configured = pentry.check_fn()
+            status_str = "configured" if configured else "not configured"
+            menu_items.append(f"{pentry.emoji} {pentry.label}  ({status_str}) [plugin]")
         menu_items.append("Done")
 
+        _total_platforms = len(_PLATFORMS) + len(_plugin_entries)
         choice = prompt_choice("Select a platform to configure:", menu_items, len(menu_items) - 1)
 
-        if choice == len(_PLATFORMS):
+        if choice == _total_platforms:
             break
 
-        platform = _PLATFORMS[choice]
+        if choice < len(_PLATFORMS):
+            platform = _PLATFORMS[choice]
 
-        if platform["key"] == "whatsapp":
-            _setup_whatsapp()
-        elif platform["key"] == "signal":
-            _setup_signal()
-        elif platform["key"] == "weixin":
-            _setup_weixin()
-        elif platform["key"] == "dingtalk":
-            _setup_dingtalk()
-        elif platform["key"] == "feishu":
-            _setup_feishu()
-        elif platform["key"] == "qqbot":
-            _setup_qqbot()
-        elif platform["key"] == "wecom":
-            _setup_wecom()
+            if platform["key"] == "whatsapp":
+                _setup_whatsapp()
+            elif platform["key"] == "signal":
+                _setup_signal()
+            elif platform["key"] == "weixin":
+                _setup_weixin()
+            elif platform["key"] == "dingtalk":
+                _setup_dingtalk()
+            elif platform["key"] == "feishu":
+                _setup_feishu()
+            elif platform["key"] == "qqbot":
+                _setup_qqbot()
+            elif platform["key"] == "wecom":
+                _setup_wecom()
+            else:
+                _setup_standard_platform(platform)
         else:
-            _setup_standard_platform(platform)
+            # Plugin platform — show env var setup instructions
+            pentry = _plugin_entries[choice - len(_PLATFORMS)]
+            print(f"\n  {pentry.label} (plugin platform)")
+            if pentry.required_env:
+                print(f"  Required env vars: {', '.join(pentry.required_env)}")
+                print(f"  Set these in ~/.hermes/.env or config.yaml gateway.platforms.{pentry.name}.extra")
+            else:
+                print(f"  Configure in config.yaml under gateway.platforms.{pentry.name}")
+            if pentry.install_hint:
+                print(f"  {pentry.install_hint}")
+            print()
 
     # ── Post-setup: offer to install/restart gateway ──
     any_configured = any(