fix(quartz): send JVM PlatformLog output to stderr

On the JVM, Log.d / .i / .w / .e were printing through \`println()\` which
lands on stdout. The amy CLI uses stdout as its JSON contract — any
Marmot/MLS command would restore state, emit a burst of DEBUG lines,
then emit the JSON object, and every caller piping through jq failed
to parse because the first non-empty line was a log line.

Switch to \`System.err.println\` inside PlatformLog.jvm.kt. Conventional
for CLIs (data on stdout, diagnostics on stderr), and the desktop app
already redirects as part of packaging. Callers who want everything
mixed can still \`2>&1\` at the shell level.

Fixes amy marmot group create / group add / message send etc. when
their output is captured by a shell script.

https://claude.ai/code/session_01M6dCKAF5Y1VyHGZPjzwDXq

quartz/src/jvmMain/kotlin/com/vitorpamplona/quartz/utils/PlatformLog.jvm.kt

@@ -34,10 +34,14 @@ actual object PlatformLog {
         message: String,
         throwable: Throwable?,
     ) {
+        // Diagnostics go to stderr so callers that pipe stdout (the CLI uses
+        // stdout for its JSON contract, desktop apps may too) aren't corrupted
+        // by log interleaving. Consumers that prefer stdout can just redirect
+        // 2>&1 at the shell level.
         if (throwable != null) {
-            println("${time()} $level: [$tag] $message. Throwable: ${throwable.message}")
+            System.err.println("${time()} $level: [$tag] $message. Throwable: ${throwable.message}")
         } else {
-            println("${time()} $level: [$tag] $message")
+            System.err.println("${time()} $level: [$tag] $message")
         }
     }