Use stable panel IDs for the editor layout

[Paaanaaamaaa]

Description

Fixes the default editor layout being broken when OvEditor is launched with a project path (which skips the Project Hub).

Fix:

• PanelWindow now derives its ID from its name ("##" + name) instead of the counter, falling back to the counter for unnamed windows so they can't collide.

Related Issue(s)

Fixes #858

Review Guidance

• Panel names passed to CreatePanel must be unique: two PanelWindows with the same name now share an ImGui window ID. They are unique today.

Screenshots

N/A

AI Usage Disclosure

None

Checklist

• My code follows the project's code style guidelines
• When applicable, I have commented my code, particularly in hard-to-understand areas
• When applicable, I have updated the documentation accordingly
• My changes don't generate new warnings or errors
• I have reviewed and take responsibility for all code in this PR (including any AI-assisted contributions)