⚡ Bolt: [performance improvement]

[dieterolson]

💡 What: Replaced Array.from({ length: N }) with pre-allocated new Array(N) and standard for loops in CSV parsing hot paths (DataExplorer and CSV parsing).
🎯 Why: In JavaScript/V8 numerical computing hot paths (like parsing large datasets), using Array.from({ length: N }, () => ...) incurs significant overhead from iterability checks, iterator creation, and closure execution per element. Pre-allocating arrays and populating them with for loops prevents O(N) intermediate garbage collection pressure and speeds up execution.
📊 Impact: Reduces intermediate object allocations and GC pauses when parsing large data CSVs, improving UI responsiveness.
🔬 Measurement: Profile the CSV upload and data explorer data preparation steps in the Chrome Performance tab to verify reduced garbage collection overhead and execution time during array initializations.

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PR created automatically by Jules for task 685097287823411952 started by @dieterolson

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[github-actions]

⚠️ SPEC.md Update Required

Source files were modified in this PR but SPEC.md was not updated.

Per the Specification-Driven Development Policy:

• Any PR that adds, removes, or changes functionality must update SPEC.md
• Update the relevant sections (features, architecture, tests, dependencies, etc.)
• Bump the Spec Version if making substantive changes

To resolve:

1. Update SPEC.md to reflect your changes, OR
2. Add the spec-exempt label if this PR genuinely doesn't affect the spec (e.g., pure refactor with no behavior change)

This check is enforced by the spec-check CI workflow.