feat: DevPanel render logging — unknown widgets, placeholders, and urlwidget failures

Add comprehensive logging to BricksRenderer for DevPanel visibility:

1. Unknown widgettypes: WARN log with full JSON dump in DevPanel Logs tab.
   Also shows [? WidgetType] orange placeholder on screen when no subwidgets.
2. Placeholder widgets (Html, MarkdownViewer, etc.): INFO log with widget summary.
3. urlwidget load failures: ERROR log with full widget JSON and error message.
4. widgetSummary(): compact one-line summary (type, id, options keys, counts).
5. widgetJsonDump(): pretty-printed JSON for deep inspection in DevPanel.

Previously: unknown widgets silently fell through to subwidget rendering.
Now: every unrecognized widget is visible in DevPanel with full context.

shared/src/commonMain/kotlin/com/bricks/mp/core/BricksRenderer.kt

@@ -27,12 +27,51 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import com.bricks.mp.actions.ActionDispatcher
+import com.bricks.mp.dev.DevLogLevel
+import com.bricks.mp.dev.DevLogSource
+import com.bricks.mp.dev.DevLogStore
 import com.bricks.mp.widgets.*
+import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.JsonPrimitive
 import kotlinx.serialization.json.JsonElement
 
+/**
+ * Serialize a widget to a compact, readable string for dev logging.
+ * Shows widgettype, id, options keys, subwidget count, and bind count.
+ */
+private fun widgetSummary(w: BricksWidget): String {
+    val optKeys = w.options.keys.joinToString(", ")
+    val subCount = w.subwidgets.size
+    val bindCount = w.binds.size
+    return buildString {
+        append("widgettype=${w.widgettype}")
+        if (w.id.isNotEmpty()) append(", id=${w.id}")
+        if (optKeys.isNotEmpty()) append(", options=[$optKeys]")
+        if (subCount > 0) append(", subwidgets=$subCount")
+        if (bindCount > 0) append(", binds=$bindCount")
+    }
+}
+
+/**
+ * Serialize the full widget JSON for detailed error inspection in DevPanel.
+ */
+private fun widgetJsonDump(w: BricksWidget): String {
+    return try {
+        val json = Json { encodeDefaults = true; prettyPrint = true }
+        json.encodeToString(BricksWidget.serializer(), w)
+    } catch (e: Exception) {
+        "Failed to serialize: ${e.message}"
+    }
+}
+
 /**
  * 递归渲染引擎 - 将 BricksWidget 树渲染为 Compose UI
+ * 
+ * Error handling strategy:
+ * - Unknown widgettypes → WARN log with full widget data in DevPanel
+ * - Placeholder widgets → INFO log with widget summary
+ * - urlwidget load failures → ERROR log with widget JSON dump
+ * - RenderPlaceholder and individual render functions handle their own errors
  */
 @Composable
 fun RenderWidget(
@@ -41,7 +80,15 @@ fun RenderWidget(
     modifier: Modifier = Modifier
 ) {
     val resolvedWidget = resolveTemplates(widget)
+    dispatchRender(resolvedWidget, actionDispatcher, modifier)
+}
 
+@Composable
+private fun dispatchRender(
+    resolvedWidget: BricksWidget,
+    actionDispatcher: ActionDispatcher?,
+    modifier: Modifier
+) {
     when (resolvedWidget.widgettype) {
         // 文本
         "Text" -> RenderTextWidget(resolvedWidget)
@@ -94,14 +141,30 @@ fun RenderWidget(
         "Message" -> RenderMessageWidget(resolvedWidget)
         "urlwidget" -> RenderUrlWidget(resolvedWidget, actionDispatcher)
 
-        // 默认: 渲染子组件
+        // 默认: 未知 widgettype — 记录日志并尝试渲染子组件
         else -> {
+            // Log unknown widgettype with full widget data for DevPanel inspection
+            DevLogStore.log(
+                level = DevLogLevel.WARN,
+                message = "Unknown widgettype: ${resolvedWidget.widgettype}",
+                details = "Widget data:\n${widgetJsonDump(resolvedWidget)}",
+                source = DevLogSource.RENDER
+            )
             if (resolvedWidget.subwidgets.isNotEmpty()) {
                 Column(modifier = modifier) {
                     resolvedWidget.subwidgets.forEach { child ->
                         RenderWidget(child, actionDispatcher)
                     }
                 }
+            } else {
+                // Show placeholder so the developer can see what was skipped
+                Text(
+                    text = "[? ${resolvedWidget.widgettype}]",
+                    color = Color(0xFFFFA000),
+                    fontSize = 10.sp,
+                    fontFamily = androidx.compose.ui.text.font.FontFamily.Monospace,
+                    modifier = Modifier.padding(4.dp)
+                )
             }
         }
     }
@@ -532,6 +595,13 @@ private fun RenderUrlWidget(widget: BricksWidget, actionDispatcher: ActionDispat
     }
 
     if (error != null) {
+        // Log the failure to DevPanel with full widget context
+        DevLogStore.log(
+            level = DevLogLevel.ERROR,
+            message = "urlwidget load failed: $url",
+            details = "Widget data:\n${widgetJsonDump(widget)}\n\nError: $error",
+            source = DevLogSource.RENDER
+        )
         Column(
             modifier = Modifier.fillMaxWidth().padding(16.dp),
             verticalArrangement = Arrangement.Center,
@@ -696,6 +766,13 @@ private fun RenderMessageWidget(widget: BricksWidget) {
 
 @Composable
 private fun RenderPlaceholder(widget: BricksWidget, name: String) {
+    // Log placeholder rendering so developers know which widgets are not yet implemented
+    DevLogStore.log(
+        level = DevLogLevel.INFO,
+        message = "Placeholder rendered: ${widget.widgettype} ($name)",
+        details = "Widget data:\n${widgetSummary(widget)}",
+        source = DevLogSource.RENDER
+    )
     Text(
         text = "[${widget.widgettype}: $name - TODO]",
         modifier = Modifier.padding(8.dp),