fix(ui): make messages layout responsive

[Victor-root]

✨ Summary

This improves the responsiveness of the WebUI Messages page.

The Messages page was previously constrained by the default DefaultPage width, which made the message list feel unnecessarily narrow on desktop screens and left a lot of available horizontal space unused.

This PR keeps the change scoped to the Messages page and preserves the existing layout for the other pages.

Fixes #744

🖥️ Desktop behavior

On larger desktop screens, the Messages page now uses more of the available horizontal space while still keeping a reasonable maximum width.

This makes long notifications, logs, Markdown content, and code blocks much easier to read without changing the overall Gotify layout.

📱 Mobile web behavior

This also improves the WebUI mobile view.

For small screens, preformatted/code blocks now wrap instead of forcing an awkward horizontal overflow. This is only about the web mobile UI, not the Android app.

Desktop/tablet behavior for code blocks is preserved: long lines can still scroll inside the code block instead of being forcibly wrapped.

🔧 Changes

• Allow DefaultPage to accept a CSS-compatible maxWidth value.
• Set a wider maxWidth only for the Messages page.
• Clamp <pre> blocks to the message card width.
• Wrap preformatted content on small screens to avoid mobile overflow.
• Leave the other pages unchanged.

✅ Tested

I tested the change locally on:

• 🖥️ Desktop
• 💻 Laptop
• 📱 Mobile web viewport

Everything works as expected:

• the Messages page uses much more available width on desktop;
• the layout remains clean on laptop/tablet-sized screens;
• mobile web no longer has broken-looking code/preformatted blocks;
• the Android app is not affected;
• existing messages, apps, clients, and WebSocket updates continue to work.

📸 Screenshots

Desktop :

Laptop :

Mobile web :