fix(ablegacy): final review I3 — default reverts to libplctag; Native is opt-in

On a wire the native PCCC path is proven only for N-file reads/writes and
one F8 read (ab_server). An absent transport key now resolves to Libplctag
for every family; explicit Native still wins and still warns once per
instance on PLC-5/LogixPccc. AdminUI dropdown, CLI help, evidence claims
(PcccFileType, AbLegacy.md wire-evidence table, release note) corrected:
S:0 (default probe) and B/T/C/R/S/L/ST/A/O/I are unverified natively.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Cli/AbLegacyCommandBase.cs

@@ -27,8 +27,9 @@ public abstract class AbLegacyCommandBase : DriverCommandBase
 
     /// <summary>Gets the transport stack used to reach the PLC.</summary>
     [CommandOption("transport", Description =
-        "Transport stack: default, native or libplctag. default = native, except libplctag for --plc-type " +
-        "Plc5 / LogixPccc (native there is PLC-5 N-file reads only, no status-bit writes, LogixPccc unverified).")]
+        "Transport stack: default, native or libplctag. default = libplctag for every --plc-type; native is " +
+        "opt-in (wire-proven only for N-file reads/writes and an F8 read; PLC-5 native is N-file reads only, " +
+        "LogixPccc unverified).")]
     public AbLegacyCliTransport Transport { get; init; } = AbLegacyCliTransport.Default;
 
     /// <summary>Gets the per-operation timeout in milliseconds.</summary>