fix(web): shrink the key pad from four rows to three

The pad ate a third of a phone screen closed and half of it open -- 271px
and 415px of 844 -- which is a poor trade above the terminal it is driving.
Five columns instead of four folds the modifiers into the arrows' spare
column, so the pad is three rows instead of four, and the presets go four
columns wide instead of three. That is 205px and 301px, and a test holds the
dock under 28% / 40% of the screen so it cannot grow back.

The inverted T is unchanged: up over down, and the empty cell now sits above
left, where a keyboard has nothing either.

The four page keys are confirmed against the real thing: on a throwaway
claude 2.1.227 pane with 300 lines of output, ESC[5~ walked the view back
242 -> 212 -> 181, ESC[1;5H jumped to the session banner and ESC[1;5F
returned to the bottom.