Placeholder Contract Audit

Compare placeholder structure across locales. A placeholder missing from a translation renders blank in some frameworks and throws in others, so the same file is a cosmetic bug in one stack and a crash in the next. ICU braces, printf conversions and mustache pairs are all recognised. Also reports a placeholder no base string supplies, a positional count that differs, a syntax that differs between locales, and unindexed printf placeholders reordered by a translation, which the renderer ignores.