⚡ Bolt: Pre-calculate derived search and date properties

[MrAlokTech]

💡 What: Added prepareSearchIndex to pre-calculate _searchStr, _isNew, and _formattedDate for all PDFs once at load time in script.js.
🎯 Why: Instantiating Date objects repeatedly inside a render/filter loop for large lists causes measurable UI slowdowns. Calculating lowercase search strings for each field of every PDF on each keystroke or filter change is also expensive and redundant.
📊 Impact: Noticeably improves UI responsiveness and list filtering performance by utilizing O(1) attribute matching and preventing per-render calculations. Reduces memory allocation rate overhead. Keep derived properties out of cache to prevent bloating.
🔬 Measurement: Verify by using UI filters/search functionality and observing improved rendering time.

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PR created automatically by Jules for task 7863543763048214725 started by @MrAlokTech

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