fix(cli): embed version via ldflags so release binaries report it

[BCook98]

Problem

The published shellcade-kit binary printed shellcade-kit (devel) / kit (unknown) for shellcade-kit version. GoReleaser builds ./cmd/shellcade-kit with plain go build, so debug.ReadBuildInfo().Main.Version is empty for the released artifact — contradicting the docs (CLAUDE.md / changeset #46) that claim "the binary embeds the same kit version it ships under".

Fix

• .goreleaser.yaml: ldflags: ["-s -w"] → ldflags: ["-s -w -X main.version={{.Version}}"], stamping the release tag into the binary.
• cmd/shellcade-kit/main.go: add a package-level var version = "dev"; in printVersion(), prefer it over the empty bi.Main.Version when set to a real value. The in-tree go build/go run path is unchanged (version stays "dev" → falls back to build info). Under lockstep the tag is the kit module release, so the kit line adopts the same version when build info can't supply one.
• .changeset/embed-cli-version.md: kit patch (a CLI-only fix rides a kit patch bump).

The "binary embeds the same kit version it ships under" claim is now true; no doc change needed.

Verification

$ go build ./cmd/shellcade-kit                  # plain build OK
$ go build -ldflags "-s -w -X main.version=v2.12.1" -o /tmp/sk ./cmd/shellcade-kit
$ /tmp/sk version
shellcade-kit v2.12.1
kit           v2.12.1 (github.com/shellcade/kit/v2)
abi           v2

In-tree fallback still degrades gracefully:

$ go run ./cmd/shellcade-kit version
shellcade-kit (devel)
kit           (unknown) (github.com/shellcade/kit/v2)
abi           v2

goreleaser check passes; go vet ./cmd/shellcade-kit and go test ./cmd/shellcade-kit pass.

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