Menu dividers under the slot 6|7 gap; debug page opens with Info Off, 5 s #174

Follow-up to #173 and the debug page (#141):

• The two-item rows' divider sits at half the row, but the slot buttons above differ in width, so it does not line up with the gap between slots 6 and 7. Put it exactly under that gap.
• The debug page opens with Info Off (only the picture) until the viewer switches it on; the snapshot interval default stays 5 s. Both choices are still remembered in the browser.