Shorten the weigh-in label to "Weight"

"Weigh-in" was the longest label in the app and, since it moved into a
third-width button, close enough to the edge to wrap on a mid-size phone.
"Weight" clears it with room to spare and loses nothing: the section, the
chart and the dialog field are all called Weight already.

EVENT_LABELS follows the button rather than only the button changing. Every
type's button label and its log label are the same string today, and weight
would have been the one exception — "⚖️ Weight" to log it, "Weigh-in" in the
history row and "Log Weigh-in" on the dialog. The prose that says "weigh-ins"
as a plural noun is left alone; it reads as English, not as a label.

The changelog entry for the rows is amended again rather than gaining a
neighbour, for the same reason as last time: it is one description of one
panel, and the rename is part of what that panel now looks like.

src/style.css

@@ -185,8 +185,8 @@ body::before {
 /* Keep the single row intact on narrow phones. */
 @media (max-width: 370px) {
   /* Three columns leave ~55px of text room on the narrowest phones, and
-     "⚖️ Weigh-in" is the longest label in the app; trimming the side padding
-     buys it back a little room before it has to wrap to two lines. */
+     "⚖️ Weight" is the longest of the three; trimming the side padding keeps
+     it on one line down to about 360px. */
   .action-row.three-up button { padding-left: 6px; padding-right: 6px; }
   .day-bar { gap: 4px; }
   .day-bar button:not(.bar-clock) { padding: 8px 7px; }
@@ -249,7 +249,7 @@ body::before {
 
 /* Quick actions: a stack of explicit rows (see index.html) instead of one
    auto-fit grid, so the grouping is the same at every width. Equal columns
-   within a row, two by default and three for the short-labelled moments. */
+   within a row, two by default and three for the dialog row at the bottom. */
 .actions {
   display: flex;
   flex-direction: column;