Fix for account screen server error

[xzzy]

No description provided.

[sentry]

Bug: The user lookup by email assigns the full EmailUser object to person_id instead of its ID, causing a ValueError on a later type conversion. It also lacks a try...except block, risking an unhandled DoesNotExist exception.
_{Severity: HIGH}

Suggested Fix

Modify the query to retrieve the user's ID directly by appending .id or .pk. Additionally, wrap the EmailUser.objects.get() call in a try...except EmailUser.DoesNotExist block to gracefully handle cases where the email does not exist in the database.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: ledger/accounts/forms.py#L215

Potential issue: When the form is initialized with an email but no ID, the code at
`ledger/accounts/forms.py:215` looks up the user. This lookup has two failure modes.
First, if a user is found, the entire `EmailUser` object is assigned to `person_id`, not
its integer ID. This object is later stringified (e.g., to 'user@example.com') and
stored in a hidden form field. When the form is submitted, an attempt to convert this
string back to an integer via `int()` will raise a `ValueError`. Second, if no user is
found for the provided email, the `EmailUser.objects.get()` call will raise an unhandled
`EmailUser.DoesNotExist` exception, causing a server error.

_{Did we get this right? 👍 / 👎 to inform future reviews.}