fix(handlers): Upload io.Copy error → 500 not 413 (B6), Me distinguishes no-rows from DB errors (B7)

backend/cmd/webui/handlers/auth.go

@@ -48,9 +48,14 @@ func (h *H) Login(c *gin.Context) {
 }
 
 func (h *H) Me(c *gin.Context) {
+	// B7: only no-rows → 401; other errors (PG down) go through dbErr → 503.
 	u, qerr := h.st.GetUserByID(c, uid(c))
 	if qerr != nil {
-		err(c, http.StatusUnauthorized, "unauthorized", "no such user")
+		if errors.Is(qerr, pgx.ErrNoRows) {
+			err(c, http.StatusUnauthorized, "unauthorized", "no such user")
+			return
+		}
+		dbErr(c, qerr)
 		return
 	}
 	c.JSON(http.StatusOK, gin.H{"id": u.ID, "username": u.Username, "role": u.Role})

backend/cmd/webui/handlers/libraries.go

@@ -146,10 +146,17 @@ func (h *H) Upload(c *gin.Context) {
 		err(c, http.StatusInternalServerError, "internal", "create tmp")
 		return
 	}
+	// B6: only MaxBytesError returns 413; other io.Copy failures (disk full,
+	// connection drop) return 500.
 	if _, e := io.Copy(out, src); e != nil {
 		out.Close()
 		os.Remove(tmp)
-		err(c, http.StatusRequestEntityTooLarge, "too_large", "upload failed")
+		var mbe *http.MaxBytesError
+		if errors.As(e, &mbe) {
+			err(c, http.StatusRequestEntityTooLarge, "too_large", "file exceeds upload limit")
+			return
+		}
+		err(c, http.StatusInternalServerError, "internal", "upload failed")
 		return
 	}
 	out.Close()