Add scan button for Big Keys and revamp Start Monitor button for Hot Keys

[ravjotbrar]

Description

Two UX improvements for the Activity view:

1. Big Keys: Add a more prominent scan/re-scan button. Currently the only way to re-trigger a scan is via the generic refresh button or the params modal. A dedicated "Scan" button would make the action more discoverable.

2. Hot Keys: Revamp the "Start Monitor" button to look more like a button and less like a link.