fix(inspect): trim before the framing check; stop advisories swallowing the backstop (#556); pin the MQTT payloadFormat mode contract (#557 item 2)

#556 item 1 — leading whitespace defeated every Inspect's pre-filter. Seven
factories (Modbus/S7/AbCip/AbLegacy/TwinCAT/FOCAS/Mqtt) tested
`reference[0] != '{'`, so a padded blob returned EMPTY and a tag the driver
refuses deployed clean. The check now trims first, matching the idiom
Sql/Calculation/MTConnect/OpcUaClient already used. The raw reference is still
what is handed to the mapper — the driver reads the stored blob, not a trimmed
copy — so the gate keeps mirroring the runtime rather than becoming lenient.
Both directions are pinned: a padded blob the mapper accepts still draws
nothing, and one that is not object-framed AFTER trimming still draws nothing
(it is not an equipment-tag TagConfig at all).

Six of the seven mappers hand the blob to a whitespace-tolerant
JsonDocument.Parse, so their verdict is unchanged by padding. MQTT is the
exception: both its readers carry the same framing gate, so a padded blob is
genuinely refused — which is why the untrimmed pre-filter was a real defect
there and not a cosmetic mismatch.

#556 item 2 — FOCAS and MQTT appended advisories unconditionally and then gated
the catch-all rejection message on `warnings.Count == 0`, so an advisory (which
fires on ACCEPTED blobs too, and says nothing about a refusal) silently
swallowed the only message naming a refusal nothing else can. The two classes
now accumulate in SEPARATE lists and the backstop gates on the rejection count
alone — structural, not string matching. MQTT's swallow was reachable in
production (a padded blob its readers refuse while every describe branch finds
the parsed document well-formed); FOCAS's backstop is currently unreachable by
audit, so its guard is protective.

#557 item 2 — decided and pinned: KEEP the union verdict. Evidence:
FromSparkplugTagConfig hard-codes PayloadFormat=Json and never consults the key;
only MqttSubscriptionManager (the Plain ingest path) decodes by it; and
MqttTagConfigModel.ToJson deliberately omits the key entirely in Sparkplug mode
(#513). So a Sparkplug driver genuinely serves the tag and rejecting it would be
stricter than the runtime. The cost — served behaviour depends on the driver's
MqttMode, which no tag row records — is paid by an ADVISORY naming the key and
the mode dependency, not by changing the verdict, so both gates keep agreeing.
The same invalid value on a blob the union REFUSES stays a rejection; the class
is decided by the accept gate, never by the key.

Falsified: reverting Modbus's trim reddens the padded-rejection theory;
neutering MQTT's backstop guard to the pre-#556 shape reddens the
advisory-plus-unnameable-rejection test; disabling the #557 advisory reddens the
contract pin; and for FOCAS, removing a describe branch alone stays green (the
backstop covers it) while additionally neutering the guard goes red.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Contracts/ModbusTagDefinitionFactory.cs

@@ -160,9 +160,15 @@ public static class ModbusTagDefinitionFactory
     public static IReadOnlyList<string> Inspect(string reference)
     {
         var warnings = new List<string>();
-        if (string.IsNullOrWhiteSpace(reference) || reference[0] != '{') return warnings;
+        // Gitea #556 item 1: the framing check TRIMS FIRST. FromTagConfig hands the blob straight to
+        // JsonDocument.Parse, which tolerates leading whitespace — so an untrimmed check let " {…}" be
+        // read (and possibly REFUSED) by the driver while drawing zero deploy warnings. A reference that
+        // still does not start with '{' after trimming is not an equipment-tag TagConfig at all and keeps
+        // drawing nothing, which is the pre-existing convention shared by all eleven inspectors.
+        if (string.IsNullOrWhiteSpace(reference) || reference.TrimStart().FirstOrDefault() != '{') return warnings;
 
-        // The accept gate: whatever the driver reads draws nothing. See the remarks.
+        // The accept gate: whatever the driver reads draws nothing. See the remarks. The RAW reference is
+        // handed to the mapper — the driver reads the stored blob, not a trimmed copy of it.
         if (FromTagConfig(reference, InspectionRawPath, out _)) return warnings;
 
         try