perf(tool): reduce edit and read memory overhead

[thdxr]

Summary

• reduce edit tool memory and I/O overhead by removing the redundant post-write reread, reusing pre-split search inputs across replacers, and switching Levenshtein to a rolling-row implementation
• make read stop after the requested page instead of scanning the rest of the file, and reject oversized image/PDF attachments before base64 encoding them
• update read tool coverage for the new truncation message and oversized attachment guard

Verification

• bun test test/tool/edit.test.ts test/tool/read.test.ts
• bun typecheck

[greptile-apps]

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