fix: string ordering operators use strcmp instead of broken single-char optimization

[cs01]

Summary

• String comparison operators (>, <, >=, <=) were incorrectly handled by the single-char literal optimization path, which only implemented ==/!= but returned wrong results for ordering operators (treating > as !=)
• Now ordering operators correctly fall through to strcmp-based comparison
• Fixes string comparisons both at top level and inside lambda/filter callbacks

Test plan

• New test fixture strings/string-comparison-operators.ts covers all ordering operators and filter lambdas
• npm run verify:quick passes

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