[arimendelow]

Fixes #304

Cause: on a spread, a page's turn zone was its outer quarter capped at 88 pt (#46). On the iPad's 1376 pt spread that cap covers only the 69 pt margin and 19 pt of text. The reviewers' taps at 7% (96 pt) and 93% (1280 pt) fell in the middle zone and toggled the controls; the build 25 log shows tap: middle at x 1279 of 1376 and x 96. The 90% taps on the iPad (1238 pt) and on the unfolded Duo (856 of 951 pt) missed the same way.

Fix: on a spread, each page now turns on its whole outer quarter, with no cap: 172 pt on the iPad, 119 pt on the unfolded Duo. A single page keeps the 88 pt cap. The middle of each page still wakes the controls; taps at 30%, 50% and 70% show them in the UI test. This narrows #46's ruling for spreads only. A spread's page turns on its margin plus the outer edge of its text, which is where the reviewers' thumbs land. A tap at 20% of the width (spazz's edge-zone-tap-0.2) still shows the controls.

A tap dropped under a jump's veil is now logged. The other half of the spazz evidence, taps that did nothing and left no log, is split out to #321.

Proof, counted in turns (MarginTapUITests, iPad Pro 13-inch, fresh open, landscape, 7 margin taps at 93/90/97/93/7/3/7%):

• Red, main plus the test: run 43282056871, MARGINTAPS turned 2 of 7. Only the 97% and 3% taps turned; the rest showed the controls.
• Green, with the fix: run 43282063116, turned 7 of 7. The three middle taps showed the controls, and none turned.
• TapZonesTests covers the 1376, 1100 and 951 pt spreads and the single page. The UI test can't unfold the Duo (see real-unfold.yml).

The new test is in the ipad-taps-rest catch-all, main only.