feat(galaxy.browser): add transient gateway-connection factory

GalaxyDriverBrowser opens an ad-hoc GalaxyRepositoryClient from the
AdminUI's persisted Galaxy options and hands it to a GalaxyBrowseSession
for the address picker. Mirrors GalaxyDriver.BuildClientOptions field-
for-field so the gateway sees an identical option shape, with API-key
resolution inlined (env:/file:/dev: prefixes) so the Browser project
needn't take a hard reference on Driver.Galaxy.

Connect phase runs under a 30s budget linked to the caller's CT and
includes a TestConnectionAsync call so auth/TLS/DNS failures surface
inside the budget instead of waiting for the first DiscoverHierarchy
round-trip. On any post-Create exception the client is disposed before
the throw propagates.

Refactored GalaxyBrowseSession to take only GalaxyRepositoryClient —
browse never needs MxGatewaySession (that's only for live subscribe/
write paths), and constructing one outside the runtime driver isn't
straightforward. The session now disposes _client in DisposeAsync; the
_session field/parameter is gone.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Browser/GalaxyBrowseSession.cs

@@ -12,11 +12,12 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Browser;
 ///     caches it by <c>TagName</c> (and <c>GobjectId</c> for parent lookup), and serves
 ///     subsequent <see cref="ExpandAsync"/> calls in-memory. Attribute fetches are
 ///     per-object via <c>DiscoverHierarchyAsync(MaxDepth=0, IncludeAttributes=true)</c>.
-///     Owns the supplied <see cref="MxGatewaySession"/> and disposes it best-effort.
+///     Owns the supplied <see cref="GalaxyRepositoryClient"/> and disposes it
+///     best-effort. (Browse does not need an <c>MxGatewaySession</c> — that's only
+///     required for live subscribe/write paths handled by the runtime driver.)
 /// </summary>
 internal sealed class GalaxyBrowseSession : IBrowseSession
 {
-    private readonly MxGatewaySession _session;
     private readonly GalaxyRepositoryClient _client;
     private readonly ConcurrentDictionary<string, GalaxyObject> _byTagName = new(StringComparer.Ordinal);
     private readonly ConcurrentDictionary<int, GalaxyObject> _byGobjectId = new();
@@ -31,15 +32,14 @@ internal sealed class GalaxyBrowseSession : IBrowseSession
     public DateTime LastUsedUtc { get; private set; } = DateTime.UtcNow;
 
     /// <summary>
-    ///     Initializes a new session wrapping a connected gateway client. The factory
-    ///     in <c>GalaxyDriverBrowser</c> (Task 9) constructs both the session and the
-    ///     repository client and hands them off here for the session's lifetime.
+    ///     Initializes a new session wrapping a connected repository client. The factory
+    ///     in <c>GalaxyDriverBrowser</c> (Task 9) constructs the client via
+    ///     <see cref="GalaxyRepositoryClient.Create"/> and hands it off here for the
+    ///     session's lifetime.
     /// </summary>
-    /// <param name="session">Gateway session to dispose when the browse closes.</param>
     /// <param name="client">Galaxy repository client to query for hierarchy and attributes.</param>
-    internal GalaxyBrowseSession(MxGatewaySession session, GalaxyRepositoryClient client)
+    internal GalaxyBrowseSession(GalaxyRepositoryClient client)
     {
-        _session = session ?? throw new ArgumentNullException(nameof(session));
         _client = client ?? throw new ArgumentNullException(nameof(client));
     }
 
@@ -186,7 +186,7 @@ internal sealed class GalaxyBrowseSession : IBrowseSession
     };
 
     /// <summary>
-    ///     Idempotently tears down the underlying gateway session. Swallows exceptions
+    ///     Idempotently tears down the underlying repository client. Swallows exceptions
     ///     on shutdown — the registry's reaper may be racing a client-initiated close.
     /// </summary>
     public async ValueTask DisposeAsync()
@@ -196,7 +196,7 @@ internal sealed class GalaxyBrowseSession : IBrowseSession
         _rootGate.Dispose();
         try
         {
-            await _session.DisposeAsync().ConfigureAwait(false);
+            await _client.DisposeAsync().ConfigureAwait(false);
         }
         catch
         {