fix(mqtt): Sparkplug array and unsupported-type metrics are not bindable from the browser (R06:M-5)

The ingestor refuses array metrics and unmapped types, yet DescribeMetric still stated
their binding tuple, so a browse-commit produced a tag stuck at
BadWaitingForInitialData forever. Those leaves now state no address (the commit
refuses them) and say why in the descriptor line.

Refs #744
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

docs/drivers/Mqtt.md

@@ -249,7 +249,10 @@ One subscription (`spBv1.0/{GroupId}/#`) feeds a per-edge-node state machine
   [Structured metrics](#structured-metrics-template--dataset--propertyset).
 - **Unsupported datatypes are skipped with a warning, never guessed**: `PropertySetList`, `Unknown`,
   extension values, and any `Template`/`DataSet` that cannot be flattened honestly. `Int8`→`Int16` and
-  `UInt8`→`UInt16` widen; `*Array` variants map to the element type with the array bit set.
+  `UInt8`→`UInt16` widen; `*Array` variants map to the element type with the array bit set — but
+  **array metrics are not read in v1** (warned once, never fed), so the browse picker offers them, and any
+  metric whose type is unsupported, **without an address**: the browse-commit refuses them rather than
+  committing a tag that waits for initial data forever (R06:M-5).
 - **Ingest state is reset at every session/authoring seam** — a reconnect or a `ReinitializeAsync`
   must not carry a previous session's alias table into a new one.