Canned response search now removes NUL bytes from user-provided search
text before passing it to PostgreSQL, so malformed input returns normal
search results instead of a database encoding error.
## Closes
-
[CW-7922](https://linear.app/chatwoot/issue/CW-7922/harden-backend-paths-causing-production-sentry-errors)
- [Sentry 7663466064](https://chatwoot-p3.sentry.io/issues/7663466064/)
## How to reproduce
Call the canned responses endpoint with a search parameter containing a
NUL byte. PostgreSQL previously raised `PG::UntranslatableCharacter`
while evaluating the search query.
## What changed
- Strip NUL bytes once at the controller boundary.
- Reuse the sanitized value for matching and result ranking.
- Add request coverage for a search term containing a NUL byte.
8842c71a90