Align Files headerbars and main content pane

[myhousece]

Summary

This PR adjusts the layout and sizing behavior of the Files window.

Changes

• Align the sidebar headerbar with the main window headerbar.
• Move the view switcher to the right side of the main headerbar.
• Reorganize the main content area so the headerbar and tab content share the same container.
• Prevent the main content pane from being shrunk below its minimum requested size.

Motivation

These changes address the current layout of the Files window and bring the headerbar arrangement closer to the structure used by Code.

The changes are limited to:

• src/View/Window.vala
• src/View/Sidebar/SidebarWindow.vala

No file-management functionality or unrelated components were changed.

Testing

• Built the project successfully with Meson.
• Installed the build into an isolated test prefix.
• Ran Files from that isolated environment using meson devenv.
• Verified the resulting interface and the main content pane resizing behavior.

No system-wide installation was used for testing.

[danirabbit]

OP this description seems written with an LLM. Can you confirm you didn't use any LLM or "AI" assistance in this pull request as outlined in our contributor guide? https://docs.elementary.io/contributor-guide

[myhousece]

OP esta descrição parece escrita com um LLM. Você pode confirmar que não usou nenhuma assistência LLM ou "AI" neste pull request, conforme descrito em nosso guia de contribuidores? https://docs.elementary.io/contribuinte-guia

Hi Danielle,

Yes, I did use ChatGPT while working on this pull request. I'm not a developer, and I used it mainly to help me understand the code and figure out how the change worked.

I honestly didn't know that using this kind of assistance wasn't allowed for contributions. I understand the policy now and I respect it.

I really like elementary OS and the project. It's the Linux project I've felt most connected to, and I've wanted to contribute somehow for a while. I was happy to be able to help, even with something small like this.

Thanks for pointing me to the contributor guide.

[danirabbit]

Thanks for being honest! Closing in accordance with our contributor guide, sorry!

[jeremypw]

@myhousece see #2509 for previous PR to do something similar and the associated issue report. It was decided to leave this until after Gtk4 porting.