Follow-up to #52979 with some
design refinements.

Release Notes:

- N/A

---------

Co-authored-by: cameron <cameron.studdstreet@gmail.com>
Co-authored-by: Anthony Eid <hello@anthonyeid.me>

…es#52979)

This PR allows users to create a new thread based off a git worktree
that already exists or has a custom name. User's can also choose what
branch they want the newly generated worktree to be based off of.

The UI still needs some polish, but I'm merging this early to get the
team using this before our preview launch. I'll be active today and
tomorrow before launch to fix any nits we have with the UI.

Functionality of this feature works! And I have a basic test to prevent
regressions


Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A or Added/Fixed/Improved ...

---------

Co-authored-by: cameron <cameron.studdstreet@gmail.com>

…industries#53324)

Follow-up to zed-industries#52979 with some
design refinements.

Release Notes:

- N/A

---------

Co-authored-by: cameron <cameron.studdstreet@gmail.com>
Co-authored-by: Anthony Eid <hello@anthonyeid.me>

Merge upstream zed-industries/zed main branch (7544515) into Helix fork.

Notable upstream changes:
- Agent V2 feature flag removal (zed-industries#52792)
- Sidebar/MultiWorkspace rework (zed-industries#53096, zed-industries#53032, zed-industries#53267)
- Agent panel git worktree/branch pickers (zed-industries#52979)
- Language model crate refactor (zed-industries#53270)
- Notification panel removal (zed-industries#50204)
- Subagent permission requests (zed-industries#53428)
- Worktree archival on thread archive (zed-industries#53215)
- Agent layout onboarding (zed-industries#52940)
- AuthRequired status for context servers (zed-industries#53396)

Conflict resolutions:
- crates/zed/Cargo.toml: kept external_websocket_sync feature + upstream track-project-leak
- crates/agent_ui/Cargo.toml: kept external_websocket_sync feature + upstream audio feature
- crates/agent_ui/src/agent_panel.rs: preserved all cfg-gated WebSocket blocks,
  migrated should_render_onboarding to should_render_new_user_onboarding,
  added upstream agent_layout_onboarding
- crates/agent/src/tools/context_server_registry.rs: added AuthRequired to match arm,
  preserved pending_tool_loads tracking
- crates/workspace/src/workspace.rs: added new upstream re-exports
- crates/title_bar/src/title_bar.rs: preserved Helix connection status indicator,
  dropped always-hidden onboarding banner (upstream removed it too)
- crates/recent_projects/src/dev_container_suggest.rs: kept suggest_dev_container check +
  upstream cli_auto_open
- .github/workflows, assets/keymaps, assets/settings, editor, multi_workspace: took upstream

Spec-Ref: helix-specs@e637a591b:001723_merge-latest-zed