fix(driver-galaxy): resolve Low code-review findings (Driver.Galaxy-005,010,012,013)

- Driver.Galaxy-005: rewrite the EventPump BoundedChannelOptions comment
  to honestly describe the Wait+TryWrite pattern.
- Driver.Galaxy-010: ResolveApiKey now warns when a literal API key is
  used in production wiring; added an explicit dev: prefix for known
  cleartext-in-dev cases and rewrote the GalaxyGatewayOptions doc.
- Driver.Galaxy-012: O(1) reverse-lookup for SubscriptionRegistry
  dispatch via per-entry FullRefByItemHandle map; immutable hash-set for
  the cross-binding reverse map; SubscribeAsync / ReadViaSubscribeOnce
  use BuildResultIndex for per-reference correlation.
- Driver.Galaxy-013: ReinitializeAsync now validates the incoming JSON
  against the running options; ReplayOnSessionLost honoured by the
  Replay path; class summary rewritten to describe the shipped surface.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Runtime/EventPump.cs

@@ -85,9 +85,14 @@ internal sealed class EventPump : IAsyncDisposable
         }
         _channel = Channel.CreateBounded<MxEvent>(new BoundedChannelOptions(channelCapacity)
         {
-            // Newest-dropped policy: when full, the producer's TryWrite returns false
-            // and we account for the drop. We do this manually rather than relying on
-            // BoundedChannelFullMode.DropWrite so we can count drops without polling.
+            // Newest-dropped semantics: we use FullMode.Wait but never call the
+            // awaitable WriteAsync — only the synchronous TryWrite below in
+            // RunAsync. With Wait + TryWrite, a full channel makes TryWrite return
+            // false immediately, which we account for via the EventsDropped counter.
+            // We deliberately do NOT use BoundedChannelFullMode.DropWrite — that
+            // would silently discard the new event inside Channel<T> without
+            // surfacing the drop on a counter (Driver.Galaxy-005: keep the comment
+            // and the FullMode value consistent).
             FullMode = BoundedChannelFullMode.Wait,
             SingleReader = true,
             SingleWriter = true,