Contact and conversation filters now reject malformed numeric/date
custom-attribute values and dangling query operators during validation,
returning the existing invalid-filter response instead of failing later
while building SQL.
## Closes
-
[CW-7922](https://linear.app/chatwoot/issue/CW-7922/harden-backend-paths-causing-production-sentry-errors)
- [Sentry 7663920842](https://chatwoot-p3.sentry.io/issues/7663920842/)
- [Sentry 7663378104](https://chatwoot-p3.sentry.io/issues/7663378104/)
## How to reproduce
Submit a custom numeric attribute filter with an empty value, or end a
filter payload with a nonblank `query_operator`. These inputs previously
reached coercion/query construction and raised production exceptions.
## What changed
- Validate numeric and date custom-attribute values before query
construction.
- Preserve presence operators, which do not require a comparison value.
- Reject a query operator on the final filter condition.
- Add contact and conversation service regression coverage.
dd203438d3