[FEATURE] Cowork: type a filesystem path into the "Project or folder" picker

Area: Desktop app (Cowork)

Problem

The "Project or folder" search box in the Claude desktop app only matches existing projects and folders that are already connected. Typing a path like ~/projects/my-app shows "No matches", so the only way to add a folder is to click "Add folder" and navigate the OS file dialog.

Proposed behavior

• When the input looks like a path (it starts with ~/, /, ./, or a Windows drive letter), treat it as a path, not a search query.
• Autocomplete directory names as the user types, with Tab to complete (like a shell or VS Code's "Open Folder").
• If the path resolves to a directory, show an "Add <path>" option at the top of the results. Pressing Enter adds it as a folder for the session, with the usual permission prompt.
• If the path doesn't exist, say so inline, for example "No such folder".

Why

• Faster for keyboard-driven users who already know where their folders are.
• Avoids clicking through deeply nested directories, hidden folders, and network mounts in the native file dialog.
• Consistent with how terminals, IDEs, and Claude Code handle paths.

Current workaround

Click "Add folder", then navigate the OS dialog. On macOS, Cmd+Shift+G in that dialog accepts a typed path, but it's an extra step, it isn't discoverable, and it conflicts with other apps that bind the same shortcut.

Related: #95464 (the same request for the Code tab's "change folder" control).