⚡ Bolt: Pre-calculate derived search and date properties

[MrAlokTech]

💡 What: Created a prepareSearchIndex function that computes _searchStr, _isNew, and _formattedDate for each PDF immediately after fetching data. Replaced inline calculation calls in renderPDFs and createPDFCard with property lookups. Added transient properties post-localStorage save to prevent cache bloat.
🎯 Why: Searching via .toLowerCase().includes() and formatting dates via new Date().toLocaleDateString() inside high-frequency render loops (renderPDFs and createPDFCard) causes severe performance bottlenecks in vanilla JS when processing large lists.
📊 Impact: Expected to reduce CPU overhead and iteration time during searches by significantly cutting object instantiation and complex string manipulations.
🔬 Measurement: Verify using the added standalone Node.js test file or by profiling renderPDFs() performance in Chrome DevTools before and after the change on large sets.

---

PR created automatically by Jules for task 12297006741696229121 started by @MrAlokTech

[cloudflare-workers-and-pages]

Deploying classnotes with    Cloudflare Pages

Latest commit:	1994ed1
Status:	✅  Deploy successful!
Preview URL:	https://8a191305.classnotes.pages.dev
Branch Preview URL:	https://bolt-precalculate-derived-pr.classnotes.pages.dev

View logs

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.