[Codex App][Remote SSH] Support multiple source folders/repositories in one project

Feature request

Local Codex projects can now include multiple source folders and repositories in one project. This is extremely useful when one product is split across separate mobile, web, backend, infrastructure, documentation, or agent repositories.

Remote SSH projects still appear to be limited to one connected host and one folder. Adding another remote repository therefore creates another top-level project in the sidebar, even when the repositories belong to the same product.

Why this matters

A typical product workspace may contain separate repositories for:

• iOS
• Android
• web/backend
• infrastructure
• shared documentation or contracts

Locally, these can now be treated as one logical Codex project. Remotely, the same setup is fragmented across several projects and conversation histories, so Codex loses the main benefit of project-level cross-repository context.

Requested behavior

Please add feature parity for Remote SSH projects:

• Allow multiple source folders or repositories in one remote project
• Support multiple folders on the same remote host as the initial version
• Let Codex read and reference all attached repositories
• Keep Git operations, branches, and worktrees isolated per repository
• Clearly show which repository a task or command is operating in
• Persist the host/folder mapping across app restarts
• Allow source folders to be added or removed after project creation

Supporting multiple hosts in one project could be a later extension. Multiple repositories on the same remote host would already solve the main workflow.

Current behavior

The local project dialog supports adding multiple source folders. The Remote SSH project dialog asks for one external host and one folder path, then adds that folder as a separate project in the sidebar.

Related broader multi-folder requests: #26338 and #27943.