fix: Use textRange for PsiElement offset access

- Replace direct startOffset/endOffset with textRange.startOffset/endOffset
- Fix range calculation in IDEUtils.kt
- Update all CV providers to use proper PsiElement text range access

Author: yangbobo2021

src/main/kotlin/ai/devchat/common/IDEUtils.kt

@@ -328,7 +328,7 @@ object IDEUtils {
         var currentIndex = 0
 
         for (descriptor in sortedDescriptors) {
-            val range = descriptor.range.shiftRight(-startOffset)
+            val range = descriptor.range.shiftRight(-this.textRange.startOffset)
             if (range.startOffset >= currentIndex) {
                 builder.append(text, currentIndex, range.startOffset)
                 builder.append(descriptor.placeholderText)

src/main/kotlin/ai/devchat/plugin/hints/DocStringCVProvider.kt

@@ -13,14 +13,14 @@ import javax.swing.Icon
 class DocStringCVProvider : ChatCVProviderBase() {
     override fun buildPayload(editor: Editor, element: PsiElement): JSONObject {
         val document = editor.document
-        val startLine = document.getLineNumber(element.startOffset)
+        val startLine = document.getLineNumber(element.textRange.startOffset)
         val lineStartOffset = document.getLineStartOffset(startLine)
-        val startOffset = if (document.text.substring(lineStartOffset, element.startOffset).isBlank()) {
+        val startOffset = if (document.text.substring(lineStartOffset, element.textRange.startOffset).isBlank()) {
             lineStartOffset
         } else {
-            element.startOffset
+            element.textRange.startOffset
         }
-        editor.selectionModel.setSelection(startOffset, null, element.endOffset)
+        editor.selectionModel.setSelection(startOffset, null, element.textRange.endOffset)
         return JSONObject(mapOf("message" to "/docstring"))
     }
 

src/main/kotlin/ai/devchat/plugin/hints/ExplainCodeCVProvider.kt

@@ -11,7 +11,7 @@ import javax.swing.Icon
 
 class ExplainCodeCVProvider : ChatCVProviderBase() {
     override fun buildPayload(editor: Editor, element: PsiElement): JSONObject {
-        editor.selectionModel.setSelection(element.startOffset, null, element.endOffset)
+        editor.selectionModel.setSelection(element.textRange.startOffset, null, element.textRange.endOffset)
         return JSONObject(mapOf("message" to "/explain"))
     }