Dispatch: add device picker for multi-machine setups

Feature Request

When using Dispatch from the iPhone app, there's no way to choose which connected machine receives the task. It goes to whichever desktop app was most recently active.

Use Case

I have two machines running Claude desktop:

• Windows laptop -- general use, research
• Mac Mini -- iOS development (Xcode, simulators, etc.)

When I Dispatch from my iPhone, I want to target a specific machine -- e.g., send a coding task to my Mac Mini, not my Windows laptop.

Proposed Solution

Add a device picker to the iPhone Dispatch UI:

• Show a list of connected/online machines by name (e.g., "David's Mac Mini", "David's Laptop")
• Allow setting a default device (optionally per project)
• Show device status (online/offline)

Why This Matters

• Multi-machine setups are common (work/personal, Windows/Mac, laptop/desktop)
• iOS developers specifically need macOS for Xcode -- Dispatch to the wrong machine means the task can't run
• As Claude Code adoption grows, users will increasingly have it installed on multiple devices

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>