Closes [#18870](https://github.com/zed-industries/zed/issues/18870)


- I like to use Zed with tab_bar off
- when the file is modified there is no indicator when tab_bar is off
- this PR aims to fix that

Thanks to @Qkessler for initial PR - #22418 

This is style decided in this discussion - #22418 
@iamnbutler @mikayla-maki [subtle style
decided](https://github.com/zed-industries/zed/pull/22418#issuecomment-2605253667)

Release Notes:
- When tab_bar is off, filename in the breadcrumbs will be the indicator
when file is unsaved.


#### Changes
- when tab_bar is off and file is dirty (unsaved)
<img width="834" alt="image"
src="https://github.com/user-attachments/assets/f205731b-c8e3-4d7a-9214-cbe706e372bf"
/>


- when tab_bar is off and file is not dirty (saved)
<img width="846" alt="image"
src="https://github.com/user-attachments/assets/88ea96eb-16a2-48e8-900d-64a921f0b5c3"
/>


- when tab_bar is on
<img width="741" alt="image"
src="https://github.com/user-attachments/assets/cc543544-9949-46ed-8e09-cdcbe2f47ab8"
/>

<img width="740" alt="image"
src="https://github.com/user-attachments/assets/8d347258-26f7-4bd7-82d4-8f23dbe63d61"
/>

Release Notes:

- Changed the highlighting of the current file to represent the current
saved state, when the tab bar is turned off.