branch_picker: Add remote icons and fix edge cases

[chirivelli]

Objective

Make the branch picker easier to scan and ensure branch creation and remote icons behave consistently across All, Local, and Remote filters.

Solution

• Group local and remote branches under their own headers in the All filter.
• Place the create-branch option above branch sections when there is no exact branch-name match.
• Resolve each remote's hosting provider from its URL and show the provider icon for branches from that remote.
• Include remote URLs in remote-workspace repository responses so arbitrary remote names work without hardcoding origin or upstream.

Edge Cases Fixed

• An exact branch can exist outside the active Local or Remote filter. The picker now checks all branches before offering to create a duplicate branch.
• A non-exact search can return fuzzy branch matches and a create action. The create action now stays at the top, before the Local and Remote section headers.
• When a filtered search has no branch matches, the create action is shown without incorrectly placing it under a Local Branches or Remote Branches header.
• Repositories can use any remote name, not only origin and upstream. Provider icons are resolved independently for every configured remote.
• Remotes hosted on an unknown or unsupported forge use the generic server icon instead of implying a desktop or a specific provider.
• Remote-workspace repositories carry the same remote-name-to-URL data as local repositories, so their branch icons follow the same provider-resolution path.

Testing

• cargo check -p git_ui --no-default-features
• Branch picker test suite (17 tests)
• git diff --check

Tested on macOS.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Showcase

The updated branch picker groups local and remote branches, keeps the create-branch action above those sections, and shows forge-specific icons for remote branches.

---

Release Notes:

• Improved branch picker filtering, grouping, branch creation suggestions, and remote-provider icons.

[ChristopherBiscardi]

thanks!