[Feature]: Dedicated "Projects Directory" setting for the Create-project default Location (decoupled from Workspace Directory) #20475

Problem or use case

"Create new project" defaults its Location to ~/orca/projects. Since #14776 (fixes #14767) the default follows Settings → Workspace Directory instead, but only once that setting has been changed from its seeded ~/orca/workspaces value.

That couples two directories that many users deliberately keep apart:

• Workspace Directory is where Orca creates worktrees (nestWorkspaces puts them under <workspaceDir>/<repo>/<branch>).
• The folder where I keep projects (~/dev/<project>/... in my case).

Pointing Workspace Directory at ~/dev to fix the Create-project default would move every new worktree into ~/dev/<repo>/<branch>, right next to my project folders. So today the only options are: retype the Location on every new project, or a symlink/junction hack (~/orca/projects → ~/dev), which then makes Orca record paths under ~/orca/projects/... that differ from the real path every other tool sees.

The resolver's own comment acknowledges the tension:

Treating that seeded value as a choice would silently relocate every existing user's projects into the worktree root, where each project would then host its own worktrees inside its working tree.

(src/main/ipc/repos/repo-creation-handlers.ts, getDefaultCreateProjectParent)

Proposed solution

Add a dedicated, optional Projects Directory setting (client default, local host):

• New GlobalSettings.projectsDir?: string, unset by default.
• getDefaultCreateProjectParent resolution order becomes:
  1. projectsDir when non-blank;
  2. otherwise the existing behaviour (configured Workspace Directory, else ~/orca/projects).
• Settings → General → a "Projects Directory" field right below Workspace Directory, with Browse, placeholder showing the effective fallback, and a short description ("Default parent folder for Create new project. Leave empty to use Workspace Directory / ~/orca/projects").

No behaviour change for anyone who leaves the field empty. Remote/SSH/runtime hosts keep resolving ~/orca/projects from the host home as they do now (a per-host override can follow later if there is demand; keeping HostSettingOverrides narrow as its docblock asks).

I have the change ready and will open a PR referencing this issue.

Alternatives or additional context

• Symlink/junction ~/orca/projects → <real folder> (the workaround from Setting “Workspace Directory” is not used for the “Create new project” default path on Windows #14767): works, but Orca persists the symlinked path, so cwd-keyed tooling (agent session memory, scripts) sees a different path than ~/dev/....
• Reuse Workspace Directory (current behaviour): forces worktrees and projects into the same tree.
• Related: Floating Workspace file path is hardcoded to AppData — no setting to change where the .md lives #15752 (Floating Workspace file path hardcoded) is the same "hardcoded ~/orca/... path without a setting" pattern.

Orca 1.4.200, macOS (arm64).