fix: case-insensitive codex model matching and edit-mode submit routing

- normalizeCodexBillingModel: lowercase input for case-insensitive matching
- billing_test: use uppercase CODEX-AUTO-REVIEW to actually test case insensitivity
- ImageStudio: pass explicit forceMode from Generate button to prevent
  image-to-image mode silently falling through to text endpoint

Co-Authored-By: Claude <noreply@anthropic.com>

Author: DeliciousBuding

database/billing.go

@@ -224,7 +224,7 @@ func normalizeBillingModelName(model string) string {
 }
 
 func normalizeCodexBillingModel(model string) (string, bool) {
-	compact := strings.NewReplacer(" ", "-", "_", "-").Replace(model)
+	compact := strings.NewReplacer(" ", "-", "_", "-").Replace(strings.ToLower(model))
 	switch {
 	case strings.Contains(compact, "gpt-5.5-pro") || strings.Contains(compact, "gpt5-5-pro") || strings.Contains(compact, "gpt5.5-pro"):
 		return "gpt-5.5-pro", true

database/billing_test.go

@@ -296,7 +296,7 @@ func TestNormalizeCodexBillingModelCodexAutoReview(t *testing.T) {
 	}{
 		{"codex-auto-review", "gpt-5.4"},
 		{"codex-auto-review-v2", "gpt-5.4"}, // variant suffix should match
-		{"codex-auto-review", "gpt-5.4"},    // case-insensitive
+		{"CODEX-AUTO-REVIEW", "gpt-5.4"},    // case-insensitive
 		{"codex_auto_review", "gpt-5.4"},    // underscores normalized
 	}
 	for _, tt := range tests {

frontend/src/pages/ImageStudio.tsx

@@ -1216,7 +1216,7 @@ export default function ImageStudio() {
               <X className="size-4" />
               {t('images.clearSelection')}
             </Button>
-            <Button disabled={submitting || !prompt.trim()} onClick={() => void submitJob()}>
+            <Button disabled={submitting || !prompt.trim()} onClick={() => void submitJob(createJobPayload(), imageToImageMode ? 'edit' : 'text')}>
               {submitting ? <Loader2 className="size-4 animate-spin" /> : <Play className="size-4" />}
               {t('images.generate')}
             </Button>