Allow edited access tokens to be set to never expire

[ShipItAndPray]

Summary

This fixes the web account token editor so an existing token can be changed to never expire.

Before this change, the edit dialog offered a "never" option, but the PATCH request omitted the expires field when 0 was selected. The server interpreted that as "leave unchanged", so the expiration could only be moved to a future timestamp, not to no expiration.

Changes included:

• send expires: 0 from the web client when the edit dialog selects "never"
• add a server regression test covering PATCH /v1/account/token with expires: 0

Closes #1693.

Validation

• git diff --check
• cd web && npm ci
• cd web && npm run lint -- --ext .js,.jsx ./src/app/AccountApi.js ./src/components/Account.jsx

Notes:

• The local Go toolchain in this environment is go1.13, while the repo declares go 1.25.0, so I did not claim a meaningful local go test run from this machine.

[binwiederhier]

Thanks