Improve search and rendering performance on the cheats index page

[Rion-Kaneshiro]

Hey, thanks for maintaining this collection. It's been super useful.

I noticed the index page at list/index.html becomes very sluggish during searches (typing a single letter freezes the UI for a noticeable moment), so I dug into app.js and made a few changes to address it. All existing functionality is preserved (favorites, modal, deep-linking via hash, URL params, keyboard shortcuts).

What was slow

With ~2,400 entries in cheatslist.json, every keystroke triggered:

1. A full re-filter of the dataset (fast, not the issue)
2. cardsGrid.innerHTML = '' followed by cloning all matching entries as DOM cards
3. Every card has an <img> requesting cover art at ?w=1024&thumb=false, so a fresh render fires up to 2,400 image requests at 1024px width

No debounce on the input meant this happened on every single character typed.

Changes

• Debounced search: 150ms after the last keystroke before filtering. Pressing Enter bypasses the debounce.
• Batched rendering with IntersectionObserver: renders 60 cards initially, then loads more as the user scrolls (sentinel-based, no library needed). Replaces the all-at-once render.
• Smaller grid thumbnails: ?w=384 for the grid, ?w=1024 is still used for the modal hero image. Roughly 80% less bandwidth and decode time per card.
• loading="lazy" + decoding="async" on every cover so the browser only fetches/decodes images near the viewport.
• Favorite toggle no longer re-renders the whole grid: it just flips the class on the affected card. (When the favorites filter is active and a card is unfavorited, it's removed instead.)
• Removed cache: 'no-store' from the data fetches so the 2.8MB cheatslist.json can actually be cached between page loads.
• Precomputed idLower / titleLower on each entry during load. These are referenced in filterEntries() and were being computed (or were absent) in the hot path.

Testing

• Loaded the full collection locally via python3 -m http.server
• Stress-tested the search with a variety of titles, IDs, and creator names
• Verified favorites persist, the modal opens/closes correctly, deep links via #PPSA01521-01.000.000 still work, the back button behaves, and URL params (?q=...&view=favorites) round-trip properly

Possible follow-ups (not in this PR)

• IndexedDB cache for cheatslist.json so the full dataset doesn't re-download when generation hashes match
• Optional virtual scrolling once the collection grows past ~5k entries

Happy to split this into smaller commits or adjust anything if you'd prefer a different approach. Cheers!

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