Add Debian packaging, Makefile, manpages, tests, and design doc

Introduces a static-binary build and Debian package (amd64/arm64) with
version/commit/date stamped via -ldflags. Ships section-1 manpages for
ctool, ctfetch, and ctail. Adds a `version` subcommand reachable as
`ctool version`, `ctool -version`, `ctool --version`, `ctool fetch
version`, `ctool tail version`, and via the ctfetch/ctail symlinks. Adds
tests covering the dispatcher, fetch/tail argument parsing, and the
formatter/helper functions. Adds a retrofit design document modelled on
the vpp-maglev one, with FRs and NFRs for each tool and the dispatcher.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/utils/utils.go

@@ -167,7 +167,7 @@ func FetchURL(url string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("HTTP %d", resp.StatusCode)
@@ -506,9 +506,7 @@ func parseCertDetails(certDER []byte) *CertDetails {
 		IsCA:                  cert.IsCA,
 	}
 
-	for _, e := range cert.EmailAddresses {
-		d.EmailSANs = append(d.EmailSANs, e)
-	}
+	d.EmailSANs = append(d.EmailSANs, cert.EmailAddresses...)
 	for _, u := range cert.URIs {
 		d.URISANs = append(d.URISANs, u.String())
 	}