feat(discord): split discord_server into discord + discord_admin tools

Split the monolithic discord_server tool (14 actions) into two:

- discord: core actions (fetch_messages, search_members, create_thread)
  that are useful for the agent's normal operation. Auto-enabled on
  the discord platform via the pipeline fix.

- discord_admin: server management actions (list channels/roles, pins,
  role assignment) that require explicit opt-in via hermes tools.
  Added to CONFIGURABLE_TOOLSETS and _DEFAULT_OFF_TOOLSETS.

toolsets.py

@@ -202,6 +202,18 @@ TOOLSETS = {
         "includes": []
     },
 
+    "discord": {
+        "description": "Discord read and participate tools (fetch messages, search members, create threads)",
+        "tools": ["discord"],
+        "includes": [],
+    },
+
+    "discord_admin": {
+        "description": "Discord server management (list channels/roles, pin messages, assign roles)",
+        "tools": ["discord_admin"],
+        "includes": [],
+    },
+
     "feishu_doc": {
         "description": "Read Feishu/Lark document content",
         "tools": ["feishu_doc_read"],
@@ -326,8 +338,8 @@ TOOLSETS = {
     "hermes-discord": {
         "description": "Discord bot toolset - full access (terminal has safety checks via dangerous command approval)",
         "tools": _HERMES_CORE_TOOLS + [
-            # Discord server introspection & management (gated on DISCORD_BOT_TOKEN via check_fn)
-            "discord_server",
+            "discord",
+            "discord_admin",
         ],
         "includes": []
     },