[FEATURE] Deep link to resume an existing Cowork session (claude://cowork/{session-id})

## Summary

Claude Desktop's documented deep links (https://support.claude.com/en/articles/14729294-open-claude-desktop-with-a-link) cover new chats, existing claude.ai chats/projects, and **new** Cowork/Code sessions — but there is no link that resumes an **existing local Cowork session** by ID.

## Ask

```
claude://cowork/{session-id}
```

Opens Claude Desktop directly to that Cowork session (or falls back to the session list for an unknown ID — same behavior `claude://claude.ai/chat/{id}` already has for invalid IDs).

## Why it should be cheap to add

- The `claude://` protocol handler and its router already exist and already resolve IDs for `claude.ai/chat/{id}`.
- Session IDs are already stable and known: `~/Library/Application Support/Claude/local-agent-mode-sessions///local_.json`.
- The app already navigates to these sessions from its own sidebar; the deep link only needs to trigger that same navigation.

## Use case

External launchers (Stream Deck, Raycast, scripts, agent dashboards) that monitor multiple Cowork sessions and want to jump to the one that needs attention. Today the only path is: open app, find session in sidebar, click.

## Related

- #50345 — same ask (resume by UUID), closed as duplicate
- #54614 — new Code session in folder via deep link
- #43943 — `claude-desktop://resume?session=`

## Platform

macOS, Claude Desktop (Cowork research preview).

Start by locating the existing claude:// protocol handler and router, especially the route that resolves claude.ai/chat/{id}. Trace how the app navigates to local Cowork sessions from its sidebar, then verify that claude://cowork/{session-id} opens a matching session and falls back to the session list for an unknown ID.

Written by the indexing model from the issue text.