fix: add Copilot-Vision-Request header for vision requests

**Problem:**
GitHub Copilot API returns 400 error "missing required Copilot-Vision-Request
header for vision requests" when requests contain image content blocks, even
though the requests are valid Claude API calls.

**Root Cause:**
The GitHub Copilot executor was not detecting vision content in requests and
did not add the required `Copilot-Vision-Request: true` header.

**Solution:**
- Added `detectVisionContent()` function to check for image_url/image content blocks
- Automatically add `Copilot-Vision-Request: true` header when vision content is detected
- Applied fix to both `Execute()` and `ExecuteStream()` methods

**Testing:**
- Tested with Claude Code IDE requests containing code context screenshots
- Vision requests now succeed instead of failing with 400 errors
- Non-vision requests remain unchanged

Fixes issue where GitHub Copilot executor fails all vision-enabled requests,
causing unnecessary fallback to other providers and 0% utilization.

Co-Authored-By: Claude (claude-sonnet-4.5) <noreply@anthropic.com>

internal/runtime/executor/github_copilot_executor.go

@@ -17,6 +17,7 @@ import (
 	cliproxyexecutor "github.com/router-for-me/CLIProxyAPI/v6/sdk/cliproxy/executor"
 	sdktranslator "github.com/router-for-me/CLIProxyAPI/v6/sdk/translator"
 	log "github.com/sirupsen/logrus"
+	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
 
@@ -134,6 +135,11 @@ func (e *GitHubCopilotExecutor) Execute(ctx context.Context, auth *cliproxyauth.
 	}
 	e.applyHeaders(httpReq, apiToken)
 
+	// Add Copilot-Vision-Request header if the request contains vision content
+	if detectVisionContent(body) {
+		httpReq.Header.Set("Copilot-Vision-Request", "true")
+	}
+
 	var authID, authLabel, authType, authValue string
 	if auth != nil {
 		authID = auth.ID
@@ -238,6 +244,11 @@ func (e *GitHubCopilotExecutor) ExecuteStream(ctx context.Context, auth *cliprox
 	}
 	e.applyHeaders(httpReq, apiToken)
 
+	// Add Copilot-Vision-Request header if the request contains vision content
+	if detectVisionContent(body) {
+		httpReq.Header.Set("Copilot-Vision-Request", "true")
+	}
+
 	var authID, authLabel, authType, authValue string
 	if auth != nil {
 		authID = auth.ID
@@ -415,6 +426,34 @@ func (e *GitHubCopilotExecutor) applyHeaders(r *http.Request, apiToken string) {
 	r.Header.Set("X-Request-Id", uuid.NewString())
 }
 
+// detectVisionContent checks if the request body contains vision/image content.
+// Returns true if the request includes image_url or image type content blocks.
+func detectVisionContent(body []byte) bool {
+	// Parse messages array
+	messagesResult := gjson.GetBytes(body, "messages")
+	if !messagesResult.Exists() || !messagesResult.IsArray() {
+		return false
+	}
+
+	// Check each message for vision content
+	for _, message := range messagesResult.Array() {
+		content := message.Get("content")
+
+		// If content is an array, check each content block
+		if content.IsArray() {
+			for _, block := range content.Array() {
+				blockType := block.Get("type").String()
+				// Check for image_url or image type
+				if blockType == "image_url" || blockType == "image" {
+					return true
+				}
+			}
+		}
+	}
+
+	return false
+}
+
 // normalizeModel is a no-op as GitHub Copilot accepts model names directly.
 // Model mapping should be done at the registry level if needed.
 func (e *GitHubCopilotExecutor) normalizeModel(_ string, body []byte) []byte {