update-go-version

Use this skill when the Go version changes. ## Files to update - `flake.nix` - `.tool-versions` - `go.mod` - `custombuild/go.mod` - `e2e/go.mod` - `k6/go.mod` - `packagetracker/go.mod.tpl` - `custombuild/cmd/authgear/Dockerfile` - `custombuild/cmd/portalx/Dockerfile` - `cmd/portal/Dockerfile` - `cmd/authgear/Dockerfile` - `once/partial.dockerfile` ## Workflow 1. Update the version in every file above. 2. Use `nix store prefetch-file` to refresh the hash in `flake.nix`. 3. Run `make go-mod-tidy`. 4. Run `make once/Dockerfile`. 5. Verify the repo still builds if the version bump changed tool behavior. ## Notes - Keep the version updates consistent across all Go modules. - Do not leave one module on the old version; that creates hard-to-debug drift.