fix: resolve negative fromindex in array indexof to prevent oob access (#265)

[cs01]

Summary

• arr.indexOf(val, -N) with negative fromIndex was using the raw negative value as the loop start index, causing out-of-bounds memory access via GEP with negative index
• Fix resolves negative indices as max(0, length + index) per JS spec, in both numeric and string array indexOf paths
• Affected two separate code paths: search.ts (numeric arrays) and string-methods.ts (string arrays dispatched via string-dispatch.ts)

Test plan

• npm run verify:quick passes (tests + Stage 1 self-hosting)
• New test: arrays/indexof-negative-fromindex.ts covers both number[] and string[] with negative, zero, positive, and very-negative fromIndex values

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