[WIP] Features/improvement -- advanced sidebar

[rneeft]

This PR adds a third sidebar state — an advanced sidebar, alongside the existing collapsed and expanded ones.
It’s inspired by the Zeus/Poseidon layout and aims to show advisor info at a glance when opening each build menu.

Refactoring
The first commits are mostly cleanup:

• Moved all sidebar state handling into sidebar/city.c.
• Centralized logic that was previously scattered across multiple files.
• This should make future sidebar changes (like this one) easier to maintain.

New behavior

• Added a new Advanced sidebar mode.
• The toggle order is now: Collapsed → Advanced → Expanded → Collapsed
• No new config options yet — everything cycles automatically.

Notes

• Still a work in progress — advisor info and layout tweaks are next.
• Feedback on the refactor and toggle flow welcome!

[Sephirex95]

Welcome to the club pal, just don't let crudelios see or we both loose our jobs 🤣

[rneeft]

Till now it is mainly just putting code elsewhere 🤔. So +1000 but then I expect to see - 1000 😕

[rneeft]

Link it with #1570