refactor(docs)!: rename CLI binary to corestack-docs

go install names binaries after the directory, so cmd/docs installed an
ambiguous `docs` binary into $GOBIN that could clobber or be clobbered
by other tools. Move it to cmd/corestack-docs, matching corestack-goose,
and update goreleaser, CI, docs and usage text. Accepted ADRs keep their
text and gain a dated rename note.

BREAKING CHANGE: `go install go.auvem.com/corestack/cmd/docs@latest`
stops resolving after the next tag; use cmd/corestack-docs. @v0.1.0
still installs the old `docs` binary.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/corestack-docs/main.go

@@ -1,4 +1,4 @@
-// Command docs creates and checks ADR and plan records. See docs/docs-format.md.
+// Command corestack-docs creates and checks ADR and plan records. See docs/docs-format.md.
 package main
 
 import (
@@ -12,8 +12,8 @@ import (
 )
 
 const usage = `usage:
-  docs new adr|plan "Title"
-  docs check [--root DIR]
+  corestack-docs new adr|plan "Title"
+  corestack-docs check [--root DIR]
 `
 
 func main() { os.Exit(run(os.Args[1:], os.Stdout, os.Stderr, time.Now())) }
@@ -32,13 +32,13 @@ func run(args []string, stdout, stderr io.Writer, now time.Time) int {
 		}
 		path, err := docs.New(".", args[1], args[2], now)
 		if err != nil {
-			fmt.Fprintf(stderr, "docs: %v\n", err)
+			fmt.Fprintf(stderr, "corestack-docs: %v\n", err)
 			return 1
 		}
 		fmt.Fprintln(stdout, path)
 		return 0
 	case "check":
-		fs := flag.NewFlagSet("docs check", flag.ContinueOnError)
+		fs := flag.NewFlagSet("corestack-docs check", flag.ContinueOnError)
 		fs.SetOutput(stderr)
 		root := fs.String("root", ".", "repository root")
 		if err := fs.Parse(args[1:]); err != nil || fs.NArg() != 0 {
@@ -49,7 +49,7 @@ func run(args []string, stdout, stderr io.Writer, now time.Time) int {
 		}
 		res, err := docs.Check(*root)
 		if err != nil {
-			fmt.Fprintf(stderr, "docs: %v\n", err)
+			fmt.Fprintf(stderr, "corestack-docs: %v\n", err)
 			return 1
 		}
 		for _, p := range res.Problems {