feat: use reference-style links in changelog instead of inline links

Moves changelog link generation from inline heading format
  ## [1.1.0](https://...) - date
to reference-style definitions at the bottom of the file
  ## [1.1.0] - date
  ...
  [Unreleased]: https://.../src/branch/main
  [1.1.0]: https://.../releases/tag/v1.1.0

This keeps headings plain, which simplifies changelog parsing (the
awk pattern in publish/action.yml now matches without special-casing
the inline URL), and follows the canonical Keep a Changelog style.

internal/vociferate/vociferate.go

@@ -25,6 +25,7 @@ var releasedSectionRe = regexp.MustCompile(`(?m)^## \[(\d+\.\d+\.\d+)\] - `)
 var linkedReleasedSectionRe = regexp.MustCompile(`(?m)^## \[(\d+\.\d+\.\d+)\](?:\([^\n)]*\))? - `)
 var unreleasedHeadingRe = regexp.MustCompile(`(?m)^## \[Unreleased\](?:\([^\n)]*\))?\n`)
 var releaseHeadingRe = regexp.MustCompile(`(?m)^## \[(\d+\.\d+\.\d+)\](?:\([^\n)]*\))? - `)
+var refLinkLineRe = regexp.MustCompile(`^\[[^\]]+\]: \S`)
 
 type Options struct {
 	// VersionFile is the path to the file that stores the current version,
@@ -412,19 +413,38 @@ func addChangelogLinks(text, repoURL string) string {
 		return text
 	}
 
-	mainURL := repoURL + "/src/branch/main"
-	text = unreleasedHeadingRe.ReplaceAllString(text, fmt.Sprintf("## [Unreleased](%s)\n", mainURL))
-
+	// Normalize headings to plain format, stripping any existing inline links.
+	text = unreleasedHeadingRe.ReplaceAllString(text, "## [Unreleased]\n")
 	text = releaseHeadingRe.ReplaceAllStringFunc(text, func(match string) string {
 		parts := releaseHeadingRe.FindStringSubmatch(match)
 		if len(parts) < 2 {
 			return match
 		}
 		version := parts[1]
-		return fmt.Sprintf("## [%s](%s/releases/tag/v%s) - ", version, repoURL, version)
+		return fmt.Sprintf("## [%s] - ", version)
 	})
 
-	return text
+	// Strip any trailing reference link block (blank lines followed by ref link lines).
+	lines := strings.Split(strings.TrimRight(text, "\n"), "\n")
+	cutAt := len(lines)
+	for i := len(lines) - 1; i >= 0; i-- {
+		if strings.TrimSpace(lines[i]) == "" || refLinkLineRe.MatchString(lines[i]) {
+			cutAt = i
+		} else {
+			break
+		}
+	}
+	text = strings.Join(lines[:cutAt], "\n") + "\n"
+
+	// Build and append reference link definitions.
+	linkDefs := []string{fmt.Sprintf("[Unreleased]: %s/src/branch/main", repoURL)}
+	for _, match := range releasedSectionRe.FindAllStringSubmatch(text, -1) {
+		if len(match) >= 2 {
+			linkDefs = append(linkDefs, fmt.Sprintf("[%s]: %s/releases/tag/v%s", match[1], repoURL, match[1]))
+		}
+	}
+
+	return strings.TrimRight(text, "\n") + "\n\n" + strings.Join(linkDefs, "\n") + "\n"
 }
 
 func parseSemver(version string) (semver, error) {