Dead config field (user decision: wire them all): the AdminUI form authors
probeTimeoutSeconds ("Admin UI probe timeout", default 5) but AbLegacyDriverProbe
never read it, so Test Connect always ran on the caller's budget. It now
tightens that budget (never raises it), the same rule as the Galaxy probe; a
non-positive value keeps the caller's budget.
Refs #738
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Replaces the bare-TCP AbLegacyDriverProbe with a two-phase probe:
Phase 1 is the existing TCP preflight; Phase 2 initialises a
LibplctagLegacyTagRuntime (Protocol.ab_eip + per-family PlcType) to
open a real PCCC-over-EIP session, using AbLegacyProbeOptions.ProbeAddress
("S:0") as the probe tag. Status-code discrimination mirrors the AbCip
probe: ErrorNotFound/ErrorNoMatch/ErrorBadDevice → Ok=true "controller
reachable"; transport errors → Ok=false "handshake failed".
Adds AbLegacyDriverProbeTests (5 unit tests, all green, 168 total).
Joseph Doherty