[Rutvik2598]

Summary

Adds a "Clear all" button to the History screen so users can wipe their entire notification history in one action. For a privacy-first app, clearing your own data should be quick and obvious.

Closes #7

What changed

The data layer already exposed clearAllLogs() end to end (NotificationLogDao → HistoryRepository → HistoryRepositoryImpl), so this PR only wires up the UI:

• HistoryViewModel — add clearAll() delegating to HistoryRepository.clearAllLogs(). No new state needed; the existing reactive historyLogs flow emits an empty list once the table clears.
• HistoryScreen — add a trash icon beside the search field (disabled when the list is empty) that opens a confirmation dialog before deleting.

Screenshots

How to test

1. Have some notification history (or seed a few entries).
2. Open History → tap the trash icon (top-right, next to search).
3. Cancel → nothing changes.
4. Clear → all entries are removed and the icon greys out (disabled when empty).

Notes

• No data/domain/DAO changes — clearAllLogs() already existed and was only used for retention pruning.
• Empty-state illustration is intentionally out of scope (tracked separately in Add empty state illustration when History or Rules lists are empty #5); the list simply renders empty after clearing.