Add By Day, By Hour, and Timing stats charts; fix symptom time tracking

[mapgie]

Summary

• Fix: Symptoms logged from the period log screen now record the time when the Symptoms category has "Track against time" enabled. syncSymptomsToTrackingLog() was always passing an empty loggedAt, silently ignoring the trackAgainstTime flag.

• Feature: Three new chart types in the Stats screen, all accessible from the "Chart type" selector:

  • "By Day" — bar chart showing how often (or average value for numeric categories) a category was logged on each day of the week (Mon–Sun). Answers: "do I get headaches most on Fridays?"
  • "By Hour" — bar chart in 2-hour slots showing when during the day a category is usually logged. Only shown when the category has "Track against time" enabled. Answers: "what time of day do my headaches happen?"
  • "Timing" — scatter plot with date on X and hour-of-day on Y, overlaying two time-tracked categories as differently-coloured dots. Makes lead/lag relationships visible — e.g. seeing that hormone logs at 8am consistently precede headache logs at 6pm on the same days.

Test plan

• Enable "Track against time" on a category (e.g. Headaches), log a few entries, open Stats and confirm "By Hour" appears in the chart type selector
• Confirm "By Day" appears for any single category and shows Mon–Sun bars
• Select two categories that both have "Track against time" enabled; confirm "Timing" appears and plots both as differently-coloured dots on the date×hour grid
• Confirm "By Hour" and "By Day" do NOT appear when two categories are selected
• For the symptom fix: enable "Track against time" on the Symptoms category, log a period with symptoms, confirm the tracking log for that day has a non-empty loggedAt time

https://claude.ai/code/session_018JqDNoQmTRpYxFJJ9kVhw8