Fix #1196: preserve @ in 2FA QR labels

[Keegil]

Bug fix — 2FA QR code label displays %40 instead of @ in the account name.

Problem

When no custom label was provided for a 2FA QR code, the app generated a default label from the username (e.g. Runbox: user@example.com). Routing the otpauth:// URI through the browser's URL constructor percent-encoded the @ character to %40, causing authenticator apps to display an ugly encoded label. Issue #1196.

Fix

• Pass the raw otpauth:// URI string directly to the QR component instead of normalising it through URL.href
• Preserves @ as-is in the QR label so authenticator apps display the address correctly

Testing

• Regression spec added covering the default username-based label format
• npx tsc -p src/tsconfig.spec.json --noEmit passes
• npm run lint passes
• npm run build succeeds

Fixes #1196