[fix] release banner: restore colorlogo (random gradient) + correct version fields

[vt128]

What

The goreleaser-built (release) binaries had a regressed --version banner. This fixes the fields and restores the logo colouring. No new release is cut — the fix lands on master and rides the next tag.

Changes

• config/build.go — bring colorlogo back (a deliberate keep: it adds real cosmetic value, unlike the dead hlog/winornot/gut), and pick one of several presets at random each run, so the banner varies on every launch.
• .goreleaser.yaml
  • GitSummary now uses the full tag ({{ .Tag }} → v0.1.2, matching git describe) instead of the v-stripped {{ .Version }} (which showed 0.1.2).
  • Inject GoVersion (it was missing). GoReleaser has no built-in go-version template var, and an ldflag value can't contain spaces (go version ... breaks linking), so use the single-token go env GOVERSION exposed via a GOVERSION env.
  • Drop GitBranch — a tag build is a detached HEAD, so it only ever showed HEAD.
• release.yml — export GOVERSION before GoReleaser.

The Makefile's own ldflags (used by make build and the Docker image, which copies a pre-built binary) are unchanged and still inject the full set.

Verified

Local goreleaser build --snapshot (no release):

✰ Build Date: 2026-06-23T...
✰ Go Version: go1.25.9        # back
✰ Git Commit: 4233d4a
✰ GitSummary: v0.1.2          # v-prefixed via {{ .Tag }}
# no "Git Branch: HEAD" line

goreleaser check passes; Docker golang:1.25 floor green; full -race green.