fix(code-review): resolve Batch 2 open findings (AbCip, AbLegacy, Galaxy, FOCAS)

- Driver.AbCip.Contracts-001: parse 'writable' from TagConfig JSON (default true) instead of hardcoding
- Driver.AbCip.Contracts-002/-003: Dt type comment; drop dead [Display]/[Range] annotations
- Driver.AbCip.Contracts-004: dedicated AbCipEquipmentTagParser test class (+15)
- Driver.AbCip-017: document Tick severity Low-fallback on Bad severity read
- Driver.AbLegacy.Contracts-002/-003/-004: isArray-scalar remarks (+tests), MaxTagBytes/ForFamily docs
- Driver.Galaxy.Browser-003 + Driver.Galaxy.Contracts-003: extract ResolveApiKey -> GalaxySecretRef (dedup)
- Driver.Galaxy-019: cache buffered-interval only on Ok + ILogger warnings + ClassifyIntervalReply (+tests)
- Driver.FOCAS.Contracts-002: thread WriteIdempotent through DiscoverAsync (+test)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasDriverOptions.cs

@@ -157,9 +157,9 @@ public sealed record FocasDeviceOptions(
 ///     <c>FocasReadWriteTests</c>). Defaults to <c>true</c>.
 /// </param>
 /// <param name="WriteIdempotent">
-///     Whether repeated writes of the same value are safe. Carried for parity; not yet
-///     threaded through to <c>DriverAttributeInfo</c> in <c>DiscoverAsync</c> (see
-///     Driver.FOCAS.Contracts-002). Defaults to <c>false</c>.
+///     Whether repeated writes of the same value are safe. Threaded through to
+///     <c>DriverAttributeInfo.WriteIdempotent</c> by <c>DiscoverAsync</c> so OPC UA
+///     clients can optimise write coalescing for idempotent tags. Defaults to <c>false</c>.
 /// </param>
 public sealed record FocasTagDefinition(
     string Name,