refactor(ui): make an event row a single open target

The row already opened the event; the tick sat on top of it, so the two
smallest targets on the page did different things a few pixels apart.
"Done" was never the only thing a reader wants to say about an event
either — status, effort and notes all live in the detail sheet.

The tick becomes a chevron: decorative, aria-hidden, and leaning towards
where the row is about to take you on hover. The full-bleed button is
the only control, so there is no second stop for anyone tabbing or using
a screen reader. Undo on a revealed ignored row stays a real button —
it is a real action with nowhere better to sit.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

src/client/styles.css

@@ -176,6 +176,13 @@ body {
     border-color: var(--color-faint);
     color: var(--color-muted);
   }
+  /* The chevron leans towards where the row is about to take you. It is the
+     only thing left on the right of a row, so it has to carry "this opens"
+     on its own. */
+  .event-row:hover .row-open {
+    transform: translateX(2px);
+    color: var(--color-ink);
+  }
   .row-check:hover {
     transform: scale(1.08);
     border-color: var(--color-muted);
@@ -212,6 +219,7 @@ body {
   }
   .row-check:hover,
   .row-check:active,
+  .event-row:hover .row-open,
   .event-row:hover .row-rail {
     transform: none;
   }