feat(referral): notify referrer by email when code is redeemed

[PanAchy]

Issue for this PR

Closes #28719

Type of change

• Bug fix

What does this PR do?

When a new user signs up using a referral link, Referral.createFromAccount successfully creates the referral row but never notifies the referrer. This PR adds a non-blocking email notification to the referrer after successful redemption.

After the DB transaction completes, the inviter workspace admin email is resolved from UserTable + AuthTable. If an email address is found, AWS.sendEmail is called with:

• Subject: "Someone used your OpenCode referral code"
• Body: "A friend signed up with your OpenCode referral code. You'll earn $5 in credits when they subscribe."

The send is non-blocking: .catch(console.error) ensures a failed email does not block or fail the referral creation.

// After successful referral transaction:
const inviterEmail = await tx
  .select({ email: AuthTable.subject })
  .from(UserTable)
  .innerJoin(
    AuthTable,
    and(
      eq(AuthTable.accountID, UserTable.accountID),
      eq(AuthTable.provider, "email"),
    ),
  )
  .where(
    and(
      eq(UserTable.workspaceID, code.workspaceID),
      eq(UserTable.role, "admin"),
      isNull(UserTable.timeDeleted),
    ),
  )
  .orderBy(asc(UserTable.timeCreated))
  .then((rows) => rows[0]?.email);

if (inviterEmail)
  await AWS.sendEmail({
    to: inviterEmail,
    subject: "Someone used your OpenCode referral code",
    body: "A friend signed up with your OpenCode referral code. You'll earn $5 in credits when they subscribe.",
  }).catch(console.error);

Only packages/console/core/src/referral.ts is changed. No schema changes, no migrations needed.

How did you verify your code works?

• Traced AWS.sendEmail usage pattern from user.ts — call signature matches.
• Confirmed AuthTable.subject holds the email address for provider = "email" rows.
• Confirmed UserTable.role = "admin" identifies workspace admins.
• Email send failure is non-blocking and does not affect referral creation.
• No automated test added for the email send path: requires live DB + SST context. The logic is verifiable by code review.

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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