Add logging to created_via_invite backward-compat fallback

[Copilot]

Summary

Addresses feedback on #1602 to add diagnostic logging when the created_via_invite column backward-compat fallback triggers during invite acceptance.

Changes:

• Added isMissingCreatedViaInviteColumnError() helper to detect schema cache mismatches (PGRST204, 42703, message substring)
• Log original insertError with requestId before retry in ensurePublicUserRowExists() and main accept flow
• Applied same pattern to registers_today metric in logsnag_insights

if (isMissingCreatedViaInviteColumnError(insertError)) {
  cloudlog({
    requestId: c.get('requestId'),
    message: 'ensurePublicUserRowExists: created_via_invite column missing, retrying without it',
    error: insertError,  // Full error object for diagnostics
  })
  const { created_via_invite: _createdViaInvite, ...fallbackPayload } = insertPayload
  ;({ error: insertError } = await supabaseAdmin.from('users').insert(fallbackPayload))
}

Test plan

• Existing test coverage in tests/user-created-via-invite.test.ts validates column behavior
• Fallback logic can be manually tested by rolling back migration 20260209014020

Screenshots

N/A - Backend logging change only

Checklist

• My code follows the code style of this project and passes bun run lint:backend && bun run lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• My change has adequate E2E test coverage.
• I have tested my code manually, and I have provided steps how to reproduce my tests

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud