feat(cli): --server <name> targeting (RFC-007 PR 3, part 1)

Global flags --server (operator-defined server name) and --graph (graph id
on a multi-graph server, requires --server) resolve to the effective
remote URI through one helper and feed the ordinary uri slot — graph
resolution and the PR-2 keyed-token URL match work unchanged; the flag is
sugar for a URI the operator already owns. Exclusive with a positional
URI and --target (loud error, never silent precedence). Unknown names
fail listing the servers that ARE defined.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/omnigraph-cli/src/operator.rs

@@ -467,6 +467,25 @@ mod tests {
         assert_eq!(config.find_server_for_url("http://other:9999"), None);
     }
 
+    #[test]
+    fn server_lookup_supports_targeting() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.yaml");
+        fs::write(
+            &path,
+            "servers:\n  intel-dev:\n    url: http://127.0.0.1:8080/\n",
+        )
+        .unwrap();
+        let config = load_operator_config_at(&path).unwrap();
+        // the --server resolution shape: bare url and graph-scoped url
+        let base = config.servers["intel-dev"].url.trim_end_matches('/');
+        assert_eq!(base, "http://127.0.0.1:8080");
+        assert_eq!(
+            format!("{base}/graphs/spike"),
+            "http://127.0.0.1:8080/graphs/spike"
+        );
+    }
+
     #[test]
     fn token_env_name_uppercases_and_underscores() {
         assert_eq!(token_env_name("intel-dev"), "OMNIGRAPH_TOKEN_INTEL_DEV");