Fix remote workspace alias resolution

[chubes4]

Summary

• Resolve workspace aliases inside the GitHub-backed remote workspace backend before looking up worktrees or primary repos.
• Add smoke coverage proving current-project works for remote reads and status calls.

Testing

• php -l inc/Workspace/RemoteWorkspaceBackend.php
• php -l tests/smoke-remote-workspace-backend.php
• php tests/smoke-remote-workspace-backend.php
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Diagnosed the remote backend alias gap, drafted the code/test changes, and ran focused local validation for Chris to review.