Add metric checkboxes to the daily counts chart

The Daily counts legend is now a Pees/Poos/Meals checkbox group, so you
can hide metrics and focus on just the ones you care about. The choice is
persisted per device, at least one metric is always kept visible, and the
y-axis and bar widths adapt to the selected metrics.

src/changelog.json

@@ -1,4 +1,5 @@
 [
+  { "date": "2026-08-02", "text": "The Daily counts chart now has Pees / Poos / Meals checkboxes so you can focus on just the metrics you care about — untick the rest to see, say, only poos; your choice is remembered" },
   { "date": "2026-08-01", "text": "Logging a pee or poo now sets off 💧/💩 fireworks that shoot up from the bottom of the screen — a little celebration you can switch off in Settings (and it honours a reduced-motion preference)" },
   { "date": "2026-08-01", "text": "Tidied the header on long names and ages — the name now truncates instead of shoving the buttons, and the age reads as a compact \"16 wk · 3 mo 3 wk\"; weight-log rows are a single line again (\"Aug 1 · 16 wk\")" },
   { "date": "2026-07-26", "text": "Added a fan-chart view of the pedigree (toggle it in the header): your dog at the centre with each generation fanning outward as a ring, so many generations fit at once without the tree sprawling sideways — tap a wedge for that dog, and repeated ancestors keep their colour" },