fix(commands): say "User not found" instead of "Selector not found"

The identity resolver's fuzzy-miss error was labelled "Selector", which is
internal jargon — the operator running `rs gain grant <vip>` or `rs kick
<user>` typed a username, not a "selector". Relabel that one message to
"User" so the chat reply reads plainly.

The sibling "Selector matched multiple records." and "Selector required."
messages are intentionally left alone for now.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

server/src/services/operatorCommandService/commands/resolvers.js

@@ -146,7 +146,7 @@ function resolveIdentitySelector(selector, records = [], options = {}) {
     ],
   });
   const results = fuse.search(query);
-  if (!results.length) return { error: buildResultError('not_found', 'Selector', candidates) };
+  if (!results.length) return { error: buildResultError('not_found', 'User', candidates) };
 
   const first = results[0];
   const second = results[1];