Drop no-op suggestions where replacement equals original

The checkpoint model sometimes "flags" a correct sentence and echoes it
verbatim as the replacement, producing a card whose before/after are
identical and whose explanation says it's already fine — a suggestion
that suggests nothing. ParseCheckpoint already dropped empty-original
items; also drop these no-ops. Awareness-only families (voice) carry an
empty replacement, so the guard only fires on the edit families.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

internal/llm/checkpoint.go

@@ -89,6 +89,14 @@ func ParseCheckpoint(raw string) ([]RawSuggestion, error) {
 		if s.Original == "" {
 			continue
 		}
+		// Drop no-ops: the model sometimes "flags" a correct sentence and echoes
+		// it verbatim as the replacement, producing a card whose before/after are
+		// identical and whose explanation says it's already fine — a suggestion
+		// that suggests nothing. Awareness-only families (voice) carry an empty
+		// replacement, so this only ever fires on the edit families.
+		if s.Replacement != "" && s.Original == s.Replacement {
+			continue
+		}
 		out = append(out, s)
 	}
 	return out, nil