Refactor the `/checknow` command response to use embeds for a more
informative display. Display available checks and rate limit status
clearly for default users, including time until the next reset.

Separate and list enabled and disabled accounts in the embed fields.
Update the "Check All" button logic to only consider enabled accounts
and rename it to "Check All Enabled".

Add handling for selecting a single disabled account, providing an embed
response explaining it is disabled and that no check was deducted.
Ensure fallback captcha settings are automatically enabled for default
users if a fallback provider is configured but settings are off.

The previous text-based response was less informative. Embeds provide
a better structure for displaying account lists and status. Users on
the default API key needed clearer feedback on their remaining checks
and rate limit status. Explicitly handling disabled accounts provides
helpful feedback and prevents users from attempting checks on accounts
they have marked as disabled. Ensuring fallback settings are active
for default users with a fallback provider improves reliability.

This change significantly improves the user experience for the
`/checknow` command, making it more intuitive and informative. It
correctly enforces rate limits and respects the disabled status of
accounts.