feat(llm): add token usage tracking with event system

- Add TokenUsageEvent data class and TokenUsageListener interface
- Make Usage data class serializable for event transmission
- Standardize topic naming convention across message bus topics
- Include session tracking and notification helper for token usage events

Author: phodal

core/src/main/kotlin/cc/unitmesh/devti/llm2/TokenUsageEvent.kt

@@ -0,0 +1,41 @@
+package cc.unitmesh.devti.llm2
+
+import cc.unitmesh.devti.llms.custom.Usage
+import com.intellij.util.messages.Topic
+import kotlinx.serialization.Serializable
+
+/**
+ * Token usage event data that will be sent when SSE stream finishes
+ */
+@Serializable
+data class TokenUsageEvent(
+    val usage: Usage,
+    val model: String? = null,
+    val sessionId: String? = null,
+    val timestamp: Long = System.currentTimeMillis()
+)
+
+/**
+ * Listener interface for token usage events
+ */
+interface TokenUsageListener {
+    /**
+     * Called when token usage data is available from LLM response
+     * 
+     * @param event The token usage event containing usage statistics
+     */
+    fun onTokenUsage(event: TokenUsageEvent)
+    
+    companion object {
+        val TOPIC = Topic.create("autodev.llm.token.usage", TokenUsageListener::class.java)
+        
+        /**
+         * Notify all subscribers about token usage
+         */
+        fun notify(event: TokenUsageEvent) {
+            com.intellij.openapi.application.ApplicationManager.getApplication().messageBus
+                .syncPublisher(TOPIC)
+                .onTokenUsage(event)
+        }
+    }
+}

core/src/main/kotlin/cc/unitmesh/devti/llms/custom/OpenAIDto.kt

@@ -4,6 +4,7 @@ import com.fasterxml.jackson.annotation.JsonAlias
 import com.fasterxml.jackson.annotation.JsonInclude
 import com.fasterxml.jackson.annotation.JsonProperty
 import com.fasterxml.jackson.databind.JsonNode
+import kotlinx.serialization.Serializable
 
 data class ChatFunctionCall(
     val name: String? = null,
@@ -27,6 +28,7 @@ data class ChatCompletionChoice(
     val finishReason: String? = null,
 )
 
+@Serializable
 data class Usage(
     @JsonProperty("prompt_tokens")
     val promptTokens: Long = 0,

core/src/main/kotlin/cc/unitmesh/devti/mcp/ui/McpConfigService.kt

@@ -19,7 +19,7 @@ interface SketchConfigListener {
     fun onSelectedToolsChanged(tools: Map<String, Set<Tool>>)
 
     companion object {
-        val TOPIC = Topic.create("SketchConfigChanged", SketchConfigListener::class.java)
+        val TOPIC = Topic.create("autodev.sketch.configChanged", SketchConfigListener::class.java)
     }
 }