Remove the walking goal

It was mine, not the user's: added unprompted alongside the Walks panel because
sleepTargetFor existed and it seemed to fit. The number came from the
"five-minute rule" — five minutes per month of age, twice a day — written from
general knowledge with no source consulted and none cited in the code.

That rule is widely repeated but is folk guidance, not a veterinary standard.
Its origin is unclear, it is contested by what evidence exists on early
exercise and joint development, and it ignores breed, terrain, lead or off-lead
and the individual dog. Drawing it as a line labelled "Goal", with a ✓ for
clearing it, stated it far more confidently than a rule of thumb earns —
particularly in an app whose entire job is otherwise to record what happened
rather than to advise.

So the target line goes, along with its legend chip, the ✓, and walkTargetFor
itself, which had no other caller. The trend keeps today against yesterday and
the average: a record, with the judgement left to whoever knows the dog.

src/changelog.json

@@ -1,4 +1,5 @@
 [
+  { "date": "2026-09-01", "text": "Removed the walking goal from the Walk trend — the dashed target line, its legend chip and the ✓ that marked a day as met. It came from the “five-minute rule” (five minutes per month of age, twice a day), which is a widely repeated rule of thumb rather than veterinary guidance, and the app was stating it more confidently than it deserved. The chart is now just a record of what you walked, against yesterday and the average" },
   { "date": "2026-09-01", "text": "The 7d / 14d / 30d buttons have moved out of the Sleep panel onto their own “Charts cover” row, just under the Log event buttons. They always set the window for every chart on the page — training, timing, sleep, walks, pees/poos/meals — but sitting inside the Sleep panel made them look like a sleep setting" },
   { "date": "2026-09-01", "text": "Dropped the “Darker = more sessions that day” caption under the training consistency grid. Tapping a cell still opens that day" },
   { "date": "2026-09-01", "text": "Dropped two hint lines: the “Based on N pee gaps…” sentence under the Timing charts, and the “Rule of thumb at this age…” one in the Walks panel. The charts above them already say it. The age-based walking goal is still there, drawn as the goal line on the Walk trend" },