docs(heidenhain): driver page, README/probe index rows, drivers rule note (#803)

docs/drivers/Heidenhain.md: read-only boundary + allowlist table, transport, config,
credential references, address grammar (fixed catalog, PLC element/byte-count rules,
DATA types incl. FF Boolean), quality table, lifecycle/health/comms loss, probe, tests,
hardware-gated items and deliberate exclusions.

Also: InitializeAsync clears surviving subscription handles (the actor re-subscribes
after every successful init, so a kept handle would double-publish).

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Heidenhain/HeidenhainDriver.cs

@@ -104,6 +104,8 @@ public sealed class HeidenhainDriver : IDriver, IReadable, ISubscribable, ITagDi
     {
         // #630: release prior device state first — a re-init must never leak a session per attempt.
         await StopDevicesAsync().ConfigureAwait(false);
+        // The actor re-subscribes after every successful init; a surviving handle would double-publish.
+        _subscriptions.Clear();
         lock (_lifecycleLock) _state = DriverState.Initializing;
         try
         {