feat(matching): add an opt-in regex keyword matching mode

Fuzzy matching compares each keyword with every word of the commit
message. A word matches if it contains the keyword's letters in order.
Thus "feat" matches "fix(delegation):" and "major" matches
"deps(majors):", which gives false minor and major versions.

The new top-level config key "matching" accepts "fuzzy" (the default)
or "regex". In regex mode every wording keyword is a Go regular
expression. The tool compiles all of them when it loads the config and
runs them against the full commit message, so "(?m)^" anchors a
pattern to the start of a line. An invalid value, an invalid pattern,
or any other config parse error in regex mode stops the tool with a
non-zero exit code. It never falls back to fuzzy matching.

Fuzzy mode does not change. The blacklist check moves into one helper
that both modes use. A replay of 15 repositories gives the same
versions as before. This change improves version precision for the
repositories that opt in.

Claude-Session: https://claude.ai/code/session_01Qq1gbqQek1Zjtofo4VDRdW

cmd/utils/version.go

@@ -166,6 +166,27 @@ func ParseExistingSemver(tagName string, currentSemver SemVer, prefixes []string
 	return semanticVersion
 }
 
+// isBlacklisted reports whether contentStr contains any blacklist term
+// (case-insensitive substring match), logging the same way every caller used
+// to log it inline. Both matching modes call this so blacklist semantics stay
+// identical between fuzzy and regex matching.
+func isBlacklisted(contentStr string, blacklist []string) bool {
+	if len(blacklist) == 0 {
+		return false
+	}
+	lowerContent := strings.ToLower(contentStr)
+	for _, blacklistTerm := range blacklist {
+		if strings.Contains(lowerContent, strings.ToLower(blacklistTerm)) {
+			Debug("Blacklisted term detected, ignoring commit", map[string]interface{}{
+				"content":        contentStr,
+				"blacklist_term": blacklistTerm,
+			})
+			return true
+		}
+	}
+	return false
+}
+
 // CheckMatches checks if any of the targets match the content
 func CheckMatches(content []string, targets []string, blacklist []string) bool {
 	contentStr := strings.Join(content, " ")
@@ -186,16 +207,8 @@ func CheckMatches(content []string, targets []string, blacklist []string) bool {
 	}
 
 	// If we have a match, check against blacklist
-	if hasMatch && len(blacklist) > 0 {
-		for _, blacklistTerm := range blacklist {
-			if strings.Contains(strings.ToLower(contentStr), strings.ToLower(blacklistTerm)) {
-				Debug("Blacklisted term detected, ignoring commit", map[string]interface{}{
-					"content":        contentStr,
-					"blacklist_term": blacklistTerm,
-				})
-				return false
-			}
-		}
+	if hasMatch && isBlacklisted(contentStr, blacklist) {
+		return false
 	}
 
 	return hasMatch