feat(galaxy): wire DiscoverPageSize and ProbeTimeoutSeconds; concurrent first-touch write lanes

Review 2026-10-21 G-5, G-6, G-8 ("wire them all").

- G-5: GatewayGalaxyHierarchySource now pages the DiscoverHierarchy RPC
  itself (DiscoverHierarchyRawAsync) at Repository.DiscoverPageSize. The
  mxaccessgw client's typed DiscoverHierarchyAsync overloads hard-code a
  5000-row page and DiscoverHierarchyOptions carries no page size, so the
  authored knob reached nothing; the raw request takes page_size on the
  wire, so it is honoured here (non-positive → 5000). The loop keeps the
  client's repeated-page-token guard.
- G-6: GalaxyDriverProbe reads ProbeTimeoutSeconds from the config and
  runs under min(caller budget, configured cap) — the knob can shorten a
  probe, never extend it past the host's budget. The TCP preflight now
  shares that deadline instead of hanging on the caller's token alone.
- G-8: GatewayGalaxyDataWriter runs a batch as one lane per distinct tag,
  concurrently and bounded at 8 (MaxConcurrentWriteLanes); same-tag
  writes keep their authored order inside one lane and results land at
  their request's index. Acks stay serial by design.
- GalaxyDriverForm: help text now says what the two knobs actually do.

Refs #735

Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Forms/GalaxyDriverForm.razor

@@ -92,7 +92,7 @@
             <div class="col-md-3">
                 <label class="form-label">Discover page size</label>
                 <InputNumber @bind-Value="_form.Galaxy.RepositoryDiscoverPageSize" @bind-Value:after="EmitAsync" class="form-control form-control-sm" />
-                <div class="form-text">Default 5000 objects per page.</div>
+                <div class="form-text">Objects per DiscoverHierarchy page the driver asks the gateway for. Default 5000.</div>
             </div>
             <div class="col-md-3">
                 <div class="form-check form-switch mt-4">
@@ -138,7 +138,7 @@
             <div class="col-md-3">
                 <label class="form-label">Admin UI probe timeout (seconds)</label>
                 <InputNumber @bind-Value="_form.Galaxy.ProbeTimeoutSeconds" @bind-Value:after="EmitAsync" class="form-control form-control-sm" />
-                <div class="form-text">Max 60. Used by Test Connect. Default 30.</div>
+                <div class="form-text">Caps the Test Connect probe deadline (the probe's own budget still applies, so this only shortens it). Max 60. Default 30.</div>
             </div>
         </div>
     </div>