Editor S13: Multi-device fan-out

[mblackman]

P2.

Promote the Devices panel (#77) multi-select push precursor into full fan-out across N selected targets.

Scope:

• Parallel install runner / push content / launch / logcat across all ticked devices
• Per-device progress + status (ok/error, last push, bytes) aggregated in one view
• Failure isolation: one device erroring does not abort the rest
• Reuses the adb wrapper (Editor S7: adb wrapper #76) and dev-listen push path (Editor S9: Hot-push content path #78)

Depends on #77 (devices panel), #78 (hot-push content). Parent: #45.