chore: rename error handling to exceptions in tree

Author: sarahhaggarty

docs/kr.tree

@@ -51,7 +51,7 @@
             <toc-element topic="control-flow.md"/>
             <toc-element topic="returns.md"/>
         </toc-element>
-        <toc-element toc-title="Error handling" topic="exceptions.md"/>
+        <toc-element topic="exceptions.md"/>
         <toc-element toc-title="Functions">
             <toc-element topic="functions.md"/>
             <toc-element toc-title="Lambdas" topic="lambdas.md"/>

docs/topics/exceptions.md

@@ -1,5 +1,7 @@
 [//]: # (title: Exceptions)
 
+<web-summary>Learn how Kotlin uses exceptions to handle runtime errors.</web-summary>
+
 Exceptions help your code run more predictably, even when runtime errors occur that could disrupt program execution.
 Kotlin treats all exceptions as _unchecked_ by default.
 Unchecked exceptions simplify the exception handling process: you can catch exceptions, but you don't need to explicitly handle or [declare](java-to-kotlin-interop.md#checked-exceptions) them.