feat: add replace subcommand with multi-pattern support

internal/replace/engine.go

@@ -0,0 +1,38 @@
+package replace
+
+import "strings"
+
+// Result captures the outcome of applying patterns to a candidate name.
+type Result struct {
+	Candidate    Candidate
+	ProposedName string
+	Matches      map[string]int
+	Changed      bool
+}
+
+// ApplyPatterns replaces every occurrence of the provided patterns within the candidate's base name.
+func ApplyPatterns(candidate Candidate, patterns []string, replacement string) Result {
+	current := candidate.BaseName
+	matches := make(map[string]int, len(patterns))
+
+	for _, pattern := range patterns {
+		if pattern == "" {
+			continue
+		}
+		count := strings.Count(current, pattern)
+		if count == 0 {
+			continue
+		}
+		current = strings.ReplaceAll(current, pattern, replacement)
+		matches[pattern] += count
+	}
+
+	changed := current != candidate.BaseName
+
+	return Result{
+		Candidate:    candidate,
+		ProposedName: current,
+		Matches:      matches,
+		Changed:      changed,
+	}
+}