* fix(server): always create requested worktrees
A slug is a preferred name, not workspace identity. Let the worktree creator suffix occupied paths and branches so duplicate and detached-slug requests still create fresh worktrees.
* fix(server): suffix occupied checkout branches
Fresh creation also applies when checkout targets are already in use. Create a suffixed branch from the requested branch instead of rejecting the request.
* test(server): align occupied branch coverage
* test(server): remove stale worktree reuse expectations
