fix: Monthly widget doesn't show multiple-day events properly #15

[P4u14]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

Fixes #15 by adding adding segmented start / middle / end backgrounds for multi-day events in the monthly widget, so that these events render as a continuous bar across day like in the in-app monthly view.

Tests performed

• tested in dark and light mode on several androidStudio virtual devices in normal and biggest fontSize
• added multiple overlapping multi-day events and single-day events that also took sometimes multiple weeks

Before & after preview

Before:

After:

Closes the following issue(s)

• Closes Monthly widget doesn't show multiple-day events properly #15

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.