Fix/multi day event rendering

[John-Swindell]

Description

Please include a summary of the changes and the related issue.

Render multi-day calendar events on every day they span

Month view grouped events only by the start day index, so an event running Mon through Thu appeared only on Monday. The grouping now iterates from the event start date through its end date and adds the event to each covered day, using UTC for all-day events (stored as midnight UTC by CalendarContract) to avoid timezone skew that made all-day events appear a day early for users west of UTC.

List view had the same flaw: groupBy keyed each event by its start day only. loadListEvents now expands each event into one entry per day it covers, sorting continuation days as midnight so the event floats to the top per the expected behavior.

Fixes #69, #116, #358

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style (formatting, new lines, etc.)
• Refactoring (no functional changes, renaming)
• Other (describe the changes):

Checklist:

• The PR is to the dev branch
• My code follows the style and architecture of the project
• I have performed a self-review of my code
• I have tested the app on an actual Android device and everything works as expected
• My changes generate no new warnings or errors
• New and existing tests pass locally with my changes
• I have commented my code, particularly in hard-to-understand areas (no, but changes is very simple)