Improve exception message formatting

- Add period at end of Handoff exception message
- Add quotes around duplicate names in configuration validation message

Author: OskarStark

src/agent/src/MultiAgent/Handoff.php

@@ -29,7 +29,7 @@ public function __construct(
         private array $when,
     ) {
         if ([] === $when) {
-            throw new InvalidArgumentException('Handoff must have at least one "when" condition');
+            throw new InvalidArgumentException('Handoff must have at least one "when" condition.');
         }
     }
 

src/ai-bundle/config/options.php

@@ -732,7 +732,7 @@
                 $multiAgentNames = array_keys($v['multi_agent'] ?? []);
                 $duplicates = array_intersect($agentNames, $multiAgentNames);
 
-                throw new \InvalidArgumentException(\sprintf('Agent names and multi-agent names must be unique. Duplicate name(s) found: %s', implode(', ', $duplicates)));
+                throw new \InvalidArgumentException(\sprintf('Agent names and multi-agent names must be unique. Duplicate name(s) found: "%s"', implode(', ', $duplicates)));
             })
         ->end()
         ->validate()