Allow editing initial HOTP counter (support migration from other authenticators)

[ddjain]

Context

When adding an HOTP (counter-based) entry—via manual entry or import—the counter is always set to 0. If the entry was exported or migrated from another app (e.g. Google Authenticator, Authy), that app may have already incremented the counter, so starting at 0 can desync and produce wrong codes.

Proposed behavior

• Let users set or change the initial counter so it matches the source (e.g. after migration).
• For example:
  • Manual entry: optional “Counter” field in Advanced when type is “Counter based”, default 0.
  • Import (otpauth URL): if the URL includes counter=..., use that value instead of forcing 0.
  • Edit: for existing HOTP entries, allow editing the counter in the entry edit UI and persist it.

Current behavior

• Manual add and import/QR flows hardcode counter: 0; the counter parsing in import/background is commented out. There is no UI to set or edit the counter.