Create log timestamps in UTC to avoid local-time races

Use getTime().utc in both message constructors, document the timezone change, and cover concurrent construction and structured formatting. Restore ordinary logging calls in the parallel writer fixture.

Validation: 32 unit tests and 29 regression tests pass. Timestamp sanitizer checks pass under UTC and non-UTC timezones. The full suite retains the known allocator reports in factory-state and allocator.

src/namespaced_logging.nim

@@ -73,6 +73,7 @@ type
     level*: Level
     err*: Option[ref Exception]
     ts*: DateTime
+      ## initLogMessage records the current instant in UTC.
     msg*: string
     additionalData*: JsonNode
 
@@ -217,12 +218,13 @@ proc initLogMessage*(
     msg: string,
     err: Option[ref Exception] = none[ref Exception](),
     additionalData: JsonNode = newJNull()): LogMessage =
+  ## Create a message with a UTC timestamp, avoiding local-time conversion.
 
   LogMessage(
     scope: scope,
     level: lvl,
     err: err,
-    ts: now(),
+    ts: getTime().utc,
     msg: msg,
     additionalData: additionalData)
 
@@ -232,12 +234,13 @@ proc initLogMessage*(
     lvl: Level,
     msg: JsonNode,
     err: Option[ref Exception] = none[ref Exception]()): LogMessage =
+  ## Create a structured message with a UTC timestamp.
 
   LogMessage(
     scope: scope,
     level: lvl,
     err: err,
-    ts: now(),
+    ts: getTime().utc,
     msg:
       if msg.hasKey("msg"): msg["msg"].getStr
       elif msg.hasKey("message"): msg["message"].getStr