Update all Go modules in backend/ and backend/_example/memory_store/ to
their latest versions (chroma 2.27, go-redis 9.21, bbolt 1.5, slack 0.27,
golang.org/x/* and others); re-tidy and re-vendor, keep the example module
in sync.
Hold github.com/go-chi/chi/v5 at v5.2.5: v5.3.0 deprecates
middleware.RealIP (IP-spoofing advisories). Switching off RealIP changes
how the client IP is derived for rate limiting and votes, which is a
security decision better made on its own rather than inside a dependency
bump.
go test -race, go vet, golangci-lint and govulncheck all clean on both
modules.
Dmitry Verkhoturov
