webui: use date in more human readable exported filename (#19939)

* webui: use date in exported filename

Move conversation naming and export to utils

update index.html.gz

* webui: move literals to message export constants file

* webui: move export naming and download back to the conversation store

* chore: update webui build output

* webui: add comments to some constants

* chore: update webui build output

tools/server/webui/src/lib/utils/conversation-utils.ts

@@ -1,6 +1,7 @@
 /**
  * Utility functions for conversation data manipulation
  */
+import type { DatabaseMessage } from '$lib/types';
 
 /**
  * Creates a map of conversation IDs to their message counts from exported conversation data