fix(studio): make Sentry initialization optional

[SamratB8]

Summary

Fixes a WinDroid Studio startup crash when the SENTRY_DSN environment variable is not configured.

Changes

• initialize WinUI before optional Sentry setup
• only initialize Sentry when a non-empty DSN is present
• make the Sentry handle nullable
• only flush and dispose Sentry when it was initialized
• preserve normal application startup and shutdown behavior

Validation

• app launches successfully without SENTRY_DSN
• main window renders correctly
• APK picker opens successfully
• cancelling the picker updates the status text
• Debug build succeeds
• Release build succeeds
• git diff --check is clean

No ADB, UI layout, APK-processing, or unrelated changes are included.