fix(dashboard): alarms feed doc row + monitor-contract comment + mid-truncation attach test

The In-process page feeds table still described the alarms page's subscription as
provider status only, contradicting the three passages updated in 7b6dfba.

The loop's catch-all comment (and the cadence bullet that repeated it) claimed the
monitor completes a subscriber's stream on restart. It does not: ClearCache pushes
snapshot_status(false) through the still-open channel, and a subscriber is only
completed-with-error on a failed TryWrite, or removed by its own disposal.

The SnapshotStatus arm's priming claim had no test behind it — every push test
attached to an untruncated feed and pushed the edge itself. ScriptedAlarmFeed now
replays an optional open sequence, and a new test attaches to a feed already
primed provider_status then snapshot_status(truncated) and asserts the banner
comes up with no edge pushed after render.

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/Pages/AlarmsPage.razor

@@ -258,10 +258,13 @@
             }
             catch
             {
-                // The monitor completes a subscriber's stream when it falls behind, and
-                // again when the monitor restarts. Both are recoverable by resubscribing;
-                // the badge and banner hold their last values in the meantime, and the
-                // resubscribe is primed with the current ones.
+                // The monitor drops a subscriber whose queue it cannot write to, completing
+                // that stream with an error; short of cancellation or disposal that is the
+                // only way this enumeration ends. A monitor restart is NOT one of them — it
+                // keeps the channel and pushes the cleared status frames through it — so this
+                // catch is the fell-behind case, recoverable by resubscribing. The badge and
+                // banner hold their last values meanwhile, and the resubscribe is primed with
+                // the current ones.
             }
 
             try