refactor: remove redundant isNougatPlus check in safeStorageContext

[SEKI-YUTA]

Type of change(s)

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

What changed and why

• Removed redundant isNougatPlus() check in safeStorageContext getter
• The isDeviceInDirectBootMode property already includes an isNougatPlus() check internally, so the outer check is unnecessary
• This is a pure refactoring change with no behavioral difference

Before:

get() = if (isNougatPlus() && isDeviceInDirectBootMode) {

After:

get() = if (isDeviceInDirectBootMode) {

Logical equivalence:

• isDeviceInDirectBootMode returns isNougatPlus() && !userManager.isUserUnlocked
• Therefore, isNougatPlus() && isDeviceInDirectBootMode simplifies to just isDeviceInDirectBootMode

Tests performed

• Verified logical equivalence of the change
• Confirmed isDeviceInDirectBootMode is used standalone in App.kt without additional isNougatPlus() check, supporting this pattern

Before & after preview

N/A (no UI changes)

Closes the following issue(s)

N/A (trivial refactoring, no issue created per contribution guidelines exception)

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.