⚡ Bolt: Pre-calculate derived search properties for faster filtering

[MrAlokTech]

💡 What: Created a prepareSearchIndex function that pre-calculates _searchStr, _isNew, and _formattedDate once per data load (from network or cache). Optimized the renderPDFs filter loop to use this pre-calculated string and early returns, preventing repeated date parsing, string concatenation, and lowercasing on every search keystroke.
🎯 Why: Searching and filtering happens constantly on the frontend. Calculating complex strings and Date math inside a .filter array iteration block for every keystroke creates CPU spikes and slows down the UI, especially for larger arrays.
📊 Impact: Shifts O(N*M) continuous UI blocking calculations (where N is PDFs and M is keystrokes) to a single O(N) calculation on load. Drastically reduces time spent in the main thread during typing/searching.
🔬 Measurement: Verify by typing rapidly in the search bar. The delay before rendering should be noticeably smoother, and JS profiler will show significantly less time spent inside renderPDFs and createPDFCard.

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PR created automatically by Jules for task 12901333783784945901 started by @MrAlokTech

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