golangci-lint v2.11.4 requires Go >= 1.25. With the workflow on 1.24,
setup-go would silently trigger an in-job auto-toolchain download
(observed in run #71: 'go: github.com/golangci/golangci-lint/v2@v2.11.4
requires go >= 1.25.0; switching to go1.25.9') adding ~3 min to every
Backend (Go) run.
Bump setup-go to 1.25 in ci.yml, backend-ci.yml, go-fuzz.yml so the
prebuilt Go is already the right version.
Also lint-fix three files that golangci-lint's goimports checker
flagged — goimports sorts/groups imports and removes unused ones,
which plain gofmt leaves alone:
- veza-backend-api/cmd/api/main.go
- veza-backend-api/internal/api/handlers/chat_handlers.go
- veza-backend-api/internal/handlers/auth_integration_test.go
