perf(share): 单题卡二维码同样提到 5px/模块

单题卡右侧卡片只有 210×255，二维码最大只能到 148px（37 模块 = 4px/模块），
缩到 480 宽照样解不出。

- QQRCardW 210 → 236、QQRCardH 255 → 300、QQRSize 150 → 190（37 模块 → 185px）
  卡片仍居中对齐（x 679、y 120），左侧文字区随 QQRCardX 派生，自动收窄 26px
- 二维码卡片绘制抽成 drawQuestionQRCard，可在测试里直接调用出图
- 新增 TestQuestionQRCardLayout：二维码必须正方形、模块 ≥5px、四边留白 ≥20px、
  居中偏差 ≤1px，TEST_PREVIEW=1 输出整卡 PNG；把 QQRSize 改回 150 立刻 FAIL

实测：二维码 185px（5px/模块）、居中偏差 0.5px、上下留白 34px；
gozxing 在 960 / 720 / 480 / 320 宽下都能解出正确链接。

route/question/share.go

@@ -913,11 +913,11 @@ const (
 	QAnswerMaxLine   = 7
 
 	// 右侧二维码卡片
-	QQRCardW = 210
+	QQRCardW = 236
-	QQRCardH = 255
+	QQRCardH = 300
 	QQRCardX = QContentX + QContentW - QQRCardW
 	QQRCardY = QContentY + (QContentH-QQRCardH)/2
-	QQRSize  = 150
+	QQRSize  = 190
 
 	// 内容区最大宽度（左侧，避开二维码卡片）
 	QTextMaxW = QQRCardX - QContentX - 30
@@ -925,6 +925,29 @@ const (
 	QWatermarkY = CardHeight - 30
 )
 
+// drawQuestionQRCard 绘制单题卡右侧的二维码卡片：二维码与提示语整体垂直居中。
+func drawQuestionQRCard(canvas *image.RGBA, user *db.User, question *db.Question, logo image.Image, fontCtx *freetype.Context) error {
+	cardRect := image.Rect(QQRCardX, QQRCardY, QQRCardX+QQRCardW, QQRCardY+QQRCardH)
+	drawRoundedRect(canvas, cardRect, color.NRGBA{245, 245, 245, 255}, 20)
+	drawRoundedRect(canvas, cardRect, ColorWhite, 20)
+
+	questionURL := fmt.Sprintf("%s/_/%s/%d", conf.App.ExternalURL, user.Domain, question.ID)
+	qr, err := generateQR(questionURL, logo, QQRSize)
+	if err != nil {
+		return err
+	}
+
+	const qrToHintGap, hintLineHeight = 30, 17
+	qrSize := qr.Bounds().Dx()
+	contentH := qrSize + qrToHintGap + hintLineHeight
+	qrX := QQRCardX + (QQRCardW-qrSize)/2
+	qrY := QQRCardY + (QQRCardH-contentH)/2
+	draw.Draw(canvas, image.Rect(qrX, qrY, qrX+qrSize, qrY+qrSize), qr, image.Point{}, draw.Over)
+
+	drawTextCentered(canvas, "扫码查看回答", QQRCardX+QQRCardW/2, qrY+qrSize+qrToHintGap+hintLineHeight, FontSizeQRHint, ColorHintGray, fontCtx)
+	return nil
+}
+
 // 单题分享图结果缓存，TTL 30 分钟，上限 16 条（1C1G 内存友好）。
 var questionShareCache = newTTLCache(16)
 
@@ -1066,27 +1089,11 @@ func QuestionShareCard(ctx context.Context) {
 	_ = textY
 
 	// 右侧二维码卡片
-	cardRect := image.Rect(QQRCardX, QQRCardY, QQRCardX+QQRCardW, QQRCardY+QQRCardH)
+	if err := drawQuestionQRCard(canvas, user, question, avImg, fontCtx); err != nil {
-	drawRoundedRect(canvas, cardRect, color.NRGBA{245, 245, 245, 255}, 20)
-	drawRoundedRect(canvas, cardRect, ColorWhite, 20)
-
-	questionURL := fmt.Sprintf("%s/_/%s/%d", conf.App.ExternalURL, user.Domain, question.ID)
-	qr, err := generateQR(questionURL, avImg, QQRSize)
-	if err != nil {
 		http.Error(ctx.ResponseWriter(), "二维码生成失败", http.StatusInternalServerError)
 		logrus.WithContext(ctx.Request().Context()).WithError(err).Error("Failed to generate QR code for question share card")
 		return
 	}
-	qrSize := qr.Bounds().Dx()
-	qrDrawX := QQRCardX + (QQRCardW-qrSize)/2
-	// 二维码与提示语整体垂直居中（已删除底部冗余的长链接，卡片更简洁）
-	const qrToHintGap, hintLineHeight = 30, 17
-	contentH := qrSize + qrToHintGap + hintLineHeight
-	qrDrawY := QQRCardY + (QQRCardH-contentH)/2
-	draw.Draw(canvas, image.Rect(qrDrawX, qrDrawY, qrDrawX+qrSize, qrDrawY+qrSize), qr, image.Point{}, draw.Over)
-
-	hintY := qrDrawY + qrSize + qrToHintGap + hintLineHeight
-	drawTextCentered(canvas, "扫码查看回答", QQRCardX+QQRCardW/2, hintY, 17, ColorHintGray, fontCtx)
 
 	// 底部水印
 	drawTextCentered(canvas, "Powered by 狼的提问箱", CardWidth/2, QWatermarkY, FontSizeFooter, ColorFooterGray, fontCtx)

route/question/share_layout_test.go

@@ -14,6 +14,7 @@ import (
 	qrcode "github.com/skip2/go-qrcode"
 
 	"github.com/tamakyi/TamaBox/internal/conf"
+	"github.com/tamakyi/TamaBox/internal/db"
 )
 
 // 分享卡测试需要一份真实字体；中文站点部署时 conf.App.FontPath 必然存在，
@@ -253,6 +254,101 @@ func TestGenerateQRModuleSizeAtLeast5(t *testing.T) {
 	}
 }
 
+// 单题卡的二维码卡片：模块必须够大、整块落在卡内、提示语不越界。
+func TestQuestionQRCardLayout(t *testing.T) {
+	requireFont(t)
+	saved := conf.App.ExternalURL
+	conf.App.ExternalURL = "https://box-dev-api.337845818.best"
+	t.Cleanup(func() { conf.App.ExternalURL = saved })
+
+	user := &db.User{Domain: "tbunread1022181904"}
+	question := &db.Question{ID: 113}
+	question.UserID = user.ID
+
+	canvas := image.NewRGBA(image.Rect(0, 0, CardWidth, CardHeight))
+	draw.Draw(canvas, canvas.Bounds(), &image.Uniform{ColorWhite}, image.Point{}, draw.Src)
+
+	fctx := freetype.NewContext()
+	fctx.SetFont(requireFont(t))
+	fctx.SetDPI(72)
+	if err := drawQuestionQRCard(canvas, user, question, nil, fctx); err != nil {
+		t.Fatal(err)
+	}
+
+	// 二维码：着墨边界必须落在卡片内且四周留白 ≥20px，模块 ≥5px
+	card := image.Rect(QQRCardX, QQRCardY, QQRCardX+QQRCardW, QQRCardY+QQRCardH)
+	minX, minY, maxX, maxY := CardWidth, CardHeight, -1, -1
+	for y := card.Min.Y; y < card.Min.Y+220; y++ {
+		for x := card.Min.X; x < card.Max.X; x++ {
+			if r, _, _, _ := canvas.At(x, y).RGBA(); r < 0x4000 {
+				if x < minX {
+					minX = x
+				}
+				if y < minY {
+					minY = y
+				}
+				if x > maxX {
+					maxX = x
+				}
+				if y > maxY {
+					maxY = y
+				}
+			}
+		}
+	}
+	if maxX < 0 {
+		t.Fatal("nothing drawn in the QR card")
+	}
+	size := maxX - minX + 1
+	if size != maxY-minY+1 {
+		t.Fatalf("QR is not square: %dx%d", size, maxY-minY+1)
+	}
+	if per := size / qrModules(t, conf.App.ExternalURL+"/_/"+user.Domain+"/113"); per < 5 {
+		t.Errorf("QR module is %dpx, want >=5", per)
+	}
+	for _, gap := range []struct {
+		name       string
+		got, limit int
+	}{
+		{"left", minX - card.Min.X, 20},
+		{"right", card.Max.X - maxX - 1, 20},
+		{"top", minY - card.Min.Y, 20},
+		{"bottom", card.Max.Y - maxY - 1, 20},
+	} {
+		if gap.got < gap.limit {
+			t.Errorf("%s margin %dpx < %dpx", gap.name, gap.got, gap.limit)
+		}
+	}
+
+	if os.Getenv("TEST_PREVIEW") != "" {
+		outDir := os.Getenv("TEST_PREVIEW_DIR")
+		if outDir == "" {
+			outDir = filepath.Join("..", "..", "outputs", "sharecard-preview")
+		}
+		if err := os.MkdirAll(outDir, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		f, err := os.Create(filepath.Join(outDir, "question-card.png"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := png.Encode(f, canvas); err != nil {
+			t.Fatal(err)
+		}
+		f.Close()
+	}
+}
+
+func qrModules(t *testing.T, content string) int {
+	t.Helper()
+	q, err := qrcode.New(content, qrcode.High)
+	if err != nil {
+		t.Fatal(err)
+	}
+	q.DisableBorder = true
+	return len(q.Bitmap())
+}
+
 // 视觉自检：TEST_PREVIEW=1 时把链接区渲成 PNG，人工确认断行与对齐。
 func TestShareCardLinkPreview(t *testing.T) {
 	if os.Getenv("TEST_PREVIEW") == "" {