proxy lease: name a backend baseline with --device-baseline #4235

The problem

A proxy lease cannot name a Simlock baseline (a saved, prepared device state). Simlock's lease.request takes baseline, but LeaseDeviceSpec has no key for it, so open through connect proxy always gets a factory device. The name --baseline is taken by diff screenshot --baseline <file>.

Proposal

Add deviceBaseline to the lease device spec, like deviceMode:

• --device-baseline <name> on open, install, reinstall, uninstall (flag key deviceBaseline), in LEASE_DEVICE_SPEC_KEYS; a blank string names nothing, a non-string is device-spec-invalid.
• A daemon refuses it with device-spec-unsupported, as for the other spec keys.
• LeaseDevice gains baseline?: { name: string; version: number }. A new lease allocated with deviceBaseline whose lease.device.baseline.name is not the requested name is released and the request fails with device-spec-unsupported, as today for a missing lease.device.
• A reused lease serves a command naming deviceBaseline only when it was allocated with the same name.
• connect proxy stores it like the other spec keys; MCP and the SDK carry it.

Simlock side: callstackincubator/simlock#1308 (task #1312). Its front maps deviceBaseline to lease.request.baseline, drops target when a baseline is named, strips the key before the daemon, and echoes data.lease.device.baseline {name, version}.

Written by an agent.