feat: Enable file editing and saving (#252)

## Summary
- Adds file writing capability to Monaco editor in the file viewer
- Implements writeFile API on the server for workspace files
- Integrates save functionality into the file viewer UI with proper
state management

## Bug Fixes (Review Feedback)
- Fixed failed save discarding edits when switching files - now checks
save result and only proceeds if successful
- Fixed refresh overwriting dirty editor state - now prompts for
confirmation before discarding edits
- Fixed save button unable to save empty files - changed check from `if
(content)` to `if (content !== undefined && content !== null)`
- Added agent edit conflict detection - when agent edits file while user
has unsaved changes, shows conflict dialog with Overwrite/Cancel options
- Fixed dialog appearing behind unpinned sidebar - increased alert
dialog z-index to z-100

## Related Issues
- Closes #251

---------

Co-authored-by: Jess Chadwick <jchadwick@gmail.com>

packages/ui/src/components/instance-info.tsx

@@ -44,6 +44,7 @@ const InstanceInfo: Component<InstanceInfoProps> = (props) => {
       variant: "warning",
       confirmLabel: t("infoView.dispose.confirm.confirmLabel"),
       cancelLabel: t("infoView.dispose.confirm.cancelLabel"),
+      dismissible: false,
     })
 
     if (!confirmed) return