⚡ Bolt: [performance improvement] Optimize string building in ConvertCodexResponseToClaude

[rschumann]

💡 What: Replaced fmt.Sprintf with direct string concatenation when building SSE events in ConvertCodexResponseToClaude. Added inline comments explaining the change.

🎯 Why: fmt.Sprintf uses runtime reflection under the hood and creates multiple unnecessary intermediate allocations per chunk. In streaming responses, this occurs hundreds or thousands of times per request. This optimization avoids reflection completely, reducing overhead and latency.

📊 Impact: Reduces memory allocations per operation. Our benchmarks show a reduction from ~3200 ns/op and 15 allocs/op to ~2400 ns/op and 13 allocs/op for single-chunk simulated conversion.

🔬 Measurement: Added BenchmarkConvertCodexResponseToClaude in internal/translator/codex/claude/codex_claude_response_bench_test.go to measure and prove the improvement. Tested using go test -bench=BenchmarkConvertCodexResponseToClaude -benchmem ./....

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PR created automatically by Jules for task 7617520286461280784 started by @rschumann

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