Redesign the history list (month groups, swipe to delete)

[SamiPr0]

Stacked on #92 (base is feat/history-heatmap; retarget to main once #92 merges).

What

• Entries are grouped under sticky month headers ("October · 5 visits"), then a light day label, instead of one card per entry.
• Flat compact rows with a divider and a chevron; tap still opens the entry details.
• Swipe left to delete with an Undo snackbar, replacing the red delete button and confirmation dialog on every row. Undo restores the entry with its swim duration/distance and subscription.
• Accessibility: rows expose a "Delete entry" custom action, since a swipe isn't available to screen readers.

Tests

Unit tests for the month/visit labels and onRestoreEntry; screen tests for swipe delete, Undo, empty state after deleting the last entry, tap not deleting, and month headers. ./gradlew check ktfmtCheck is green locally. No emulator run and no device check (connectedDebugAndroidTest not run).

Note

Deleting no longer asks for confirmation; the Undo snackbar is the safety net.

🤖 Generated with Claude Code

[SamiPr0]

Superseded by #96, which combined this stack and is merged into main (cbab128). Closing; the branch is left in place.