TOTP generation fails when Base32 secret is not properly padded (missing padding handling)

### Describe the issue

TOTP generation is unable to handle padding on secret keys that aren't mod 8 via QRCodes.

To reproduce:
- Import TOTP via QR code that isn't mod 8 or is padded to be mod 8
- Compare the generated TOTP with other authenticators (Google, Microsoft, Authy)
- The codes won't match due to missing padding

Example secrets that won't scan correctly:
otpauth://totp/Example:User?secret=J3WWIV3PTGJPQV5QAICM&issuer=Example
otpauth://totp/Example:User?secret=J3WWIV3PTGJPQV5QAICM====&issuer=Example

### Browser

Chrome

### Browser Version

149.0.7827.156

### Extension Version

8.0.2

Start by reproducing the QR-code import with the two otpauth example URIs, then trace the secret through the import and TOTP generation paths. Compare the generated codes with Google, Microsoft, or Authy for both unpadded and padded secrets; done means the codes match in both cases and the behavior has regression coverage.

Written by the indexing model from the issue text.