* Enforce one pending invitation per email across all families
Users can only belong to one family, so allowing the same email to have
pending invitations from multiple families leads to ambiguous behavior.
Add a `no_other_pending_invitation` validation on create to prevent this.
Accepted and expired invitations from other families are not blocked.
Fixes#1172https://claude.ai/code/session_016fGqgha18jP48dhznm6k4m
* Normalize email before validation and use case-insensitive lookup
When ActiveRecord encryption is not configured, the email column stores
raw values preserving original casing. The prior validation used a direct
equality match which would miss case variants (e.g. Case@Test.com vs
case@test.com), leaving a gap in the cross-family uniqueness guarantee.
Fix by:
1. Adding a normalize_email callback that downcases/strips email before
validation, so all new records store lowercase consistently.
2. Using LOWER() in the SQL query for non-encrypted deployments to catch
any pre-existing mixed-case records.
https://claude.ai/code/session_016fGqgha18jP48dhznm6k4m
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Co-authored-by: Claude <noreply@anthropic.com>
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