Fix `--no-emit-workspace` with `--all-packages` on single-member workspaces (#18098)
Closes https://github.com/astral-sh/uv/issues/18070
Fixes an issue where `--no-emit-workspace --all-packages` would
incorrectly emit `-e .` (the workspace root) when the workspace
contained only a single member at the root.
When a workspace contains a single member at the root, that member is
not included in the lockfile's `members` set (it's empty). The
`--all-packages` flag uses `InstallTarget::Workspace`, which returned
`None` for `project_name()`. This meant `include_package()` had no way
to identify the root project as a workspace member — neither the
`project_name` check nor the `members.contains()` check could match it,
so it passed through the `--no-emit-workspace` filter.
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Co-authored-by: Claude <noreply@anthropic.com>