Adds Manager.telnetPreflight that dials port 17000, captures the banner,
and runs `getpdo CurrentSystemConfiguration` to read back the device's
live URL configuration. Errors are recorded on TelnetProbeError instead
of returned, so the probe is best-effort and never breaks summary
construction.
This is the data-gathering layer that the four already-declared
TelnetReachable / TelnetBanner / TelnetVerifiedConfig / TelnetProbeError
fields on MigrationSummary were waiting for. Subsequent iterations wire
the preflight into GetMigrationSummary (in parallel with SSH) and use
TelnetVerifiedConfig as a SSH-free signal for "already migrated".
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Tobias GesellchenandClaude Opus 4.7