Focus a text field when the edit dialog opens, never the date input

showModal() with no explicit focus autofocuses the first control — the
date input — which on iOS pops the native calendar over the form. Focus
weight/grams/note per event type instead, like openNoteDialog does.

src/changelog.json

@@ -1,4 +1,5 @@
 [
+  { "date": "2026-07-15", "text": "Editing an event no longer pops the date picker over the whole screen on iPhone" },
   { "date": "2026-07-15", "text": "Weight and amount fields no longer show up on events that don't use them (e.g. editing a pee)" },
   { "date": "2026-07-15", "text": "The date in the top bar is shorter (no year), so the whole bar fits on smaller iPhones" },
   { "date": "2026-07-13", "text": "The big timer is back at the top — scroll past it and it hops into the frozen bar instead" },