Fix incomplete unencrypted backup for EncOTPStorage entries

[khoazero123]

Summary

• Fix backupGetExport() skipping EncOTPStorage entries when creating plaintext backups (fixes Unencrypted backup is incomplete #1445).
• Normalize OTP type/algorithm on decrypt and export so numeric enum values (e.g. 1 for TOTP) are exported as name strings and included in otpauth text backups.
• Harden getOneLineOtpBackupFile() to handle numeric types for already-exported data.

Root cause

Some encrypted entries store type as a numeric enum. After decryption/export, those entries could remain as numbers. The otpauth exporter only accepted string types like "totp", so affected accounts were silently omitted from unencrypted backups even though they appeared in the UI after unlock.

Test plan

• Unlock extension with passphrase-protected EncOTPStorage entries (including entries that previously failed to export).
• Download unencrypted otpauth backup and confirm all unlocked accounts are present.
• Verify encrypted JSON backup still includes EncOTPStorage entries unchanged.
• Confirm TOTP/HOTP codes still generate correctly after unlock.
• Run unit tests: npm test (includes new otp-normalize.test.ts).