[BUG] Settings purge should only remove SecuScan localStorage keys

[utksh1]

Problem

Settings.handleNuclearPurge() currently calls localStorage.clear(). That removes every key for the origin, including unrelated app state that SecuScan does not own.

Expected behavior

The purge action should remove only SecuScan-owned keys, for example keys prefixed with secuscan and known app keys such as sidebar-expanded.

Acceptance criteria

• Replace broad localStorage.clear() with targeted removal of SecuScan-owned keys.
• Keep the existing confirmation modal and reload behavior.
• Add or update a focused unit test proving unrelated localStorage keys are preserved.

[vedasingh00-rgb]

I would like to work on this issue. Can you please assign this issue to me?