Fix lock_device: refuse when elicitation unavailable

lock_device shared the confirm_write() fallback which returns True
when the client doesn't support elicitation. This meant lock could
proceed silently without user consent — confirmed by accidentally
locking a real device.

Now lock_device has its own strict path that returns an error when
elicitation fails, rather than falling through.

src/cp210x_mcp/server.py

@@ -325,15 +325,24 @@ async def lock_device(device_index: int = 0, ctx: Context = None) -> dict:
             f"will be frozen forever."
         )
 
-        if ctx:
-            confirmed = await confirm_write(ctx, info)
-        else:
-            # No context = no way to confirm, refuse
+        if not ctx:
             return {
                 "error": "Lock requires interactive confirmation",
                 "message": "This operation is too dangerous without user confirmation.",
             }
 
+        # Strict confirmation — do NOT fall back to True on failure.
+        # Unlike regular writes, an irreversible lock must get explicit consent.
+        try:
+            result = await ctx.elicit(info, ["Confirm", "Cancel"])
+            confirmed = isinstance(result, AcceptedElicitation) and result.data == "Confirm"
+        except Exception:
+            return {
+                "error": "Lock requires elicitation support",
+                "message": "Your MCP client does not support elicitation. "
+                "Lock is too dangerous to proceed without explicit confirmation.",
+            }
+
         if not confirmed:
             return {"cancelled": True, "message": "Lock cancelled by user"}