Side Panel File Navigator

**User Story:**
As a user who is authoring in a document, I would like an easier way to access my other documents without having to go back into the file navigator window.

**Acceptance Criteria**
**Non-functional**
- user is able to access directory in a side panel while in document
- side panel consists of the files/directory the user is currently in

**Functional**
- documents of current directory are listed
- user is able to up level the file navigator to find what they are looking for
- when a user selects a document, document will open in a new tab
- while on a file line item, user is able to select a copy button, which copies the file path URL to clipboard (ex: user is building a page but needs to reference a particular fragment, no more going back to find fragment, preview, get link, go back to page, paste it)

https://github.com/user-attachments/assets/83f04aa0-64dd-4676-8c97-382b558fb3f4

Start by locating the existing file navigator window and document tab behavior. Trace how the current directory and document selection are represented, then determine how a side panel could expose the current directory, parent navigation, opening documents in new tabs, and copying file path URLs. Done means all listed acceptance criteria work together while authoring in a document.

Written by the indexing model from the issue text.