fix(mcp): move discovery out of model_tools import side effect (#16856) (#16899)

model_tools.py ran discover_mcp_tools() as a module-level side effect.
discover_mcp_tools() uses a blocking 120s wait internally (via
_run_on_mcp_loop -> future.result(timeout=120)).

The gateway lazy-imports run_agent -> model_tools on the first user
message, which happens inside the asyncio event loop thread.  A slow or
unreachable MCP server therefore froze Discord shard heartbeats and
Telegram polling for up to 120s on the first message after gateway
start.

Fix: remove the module-level call.  Every entry point now runs
discovery explicitly at its own startup, using the context-appropriate
blocking/non-blocking pattern:

- gateway/run.py:       loop.run_in_executor(None, discover_mcp_tools)
                        before platforms start accepting traffic
- hermes_cli/main.py:   inline (no event loop at CLI startup)
- tui_gateway/entry.py: inline (sync stdin loop, no event loop)
- acp_adapter/entry.py: inline before asyncio.run()

Closes #16856.

hermes_cli/main.py

@@ -10193,6 +10193,17 @@ Examples:
             logger.debug(
                 "plugin discovery failed at CLI startup", exc_info=True,
             )
+        try:
+            # MCP tool discovery — no event loop running in CLI/TUI startup,
+            # so inline is safe.  Moved here from model_tools.py module scope
+            # to avoid freezing the gateway's event loop on its first message
+            # via the same lazy import path (#16856).
+            from tools.mcp_tool import discover_mcp_tools
+            discover_mcp_tools()
+        except Exception:
+            logger.debug(
+                "MCP tool discovery failed at CLI startup", exc_info=True,
+            )
         try:
             from hermes_cli.config import load_config
             from agent.shell_hooks import register_from_config