[perf] Fix mobile LCP, accessibility and dead code from PageSpeed report

[duxi90]

Acts on the mobile PageSpeed report for cppserbia.org (report): Performance 70 / Accessibility 86 / Best Practices 100 / SEO 92.

The performance score decomposed as FCP 10/10 + LCP 0/25 + TBT 30/30 + CLS 25/25 + SI 5/10 — TBT and CLS were already perfect, so the entire 30-point gap was LCP (15.8 s) and Speed Index (5.6 s). Both traced to a single file.

The LCP element was the hero wallpaper div. wallpaper.png is 2,560,981 B at 6144×3456, painted into a ~412 px viewport at 40 % opacity — 83 % of the 3,101 KiB page. As a CSS background it couldn't be optimised, couldn't carry fetchpriority, and wasn't discoverable until CSS parsed.

Measured effect

	Before	After
LCP resource	2,560,981 B PNG	4,420 B AVIF
Total page transfer	3,101 KiB	203 KiB
<a> nested in <button>	5	0
Smallest flagged tap target	20 px tall	44 px
Locale routes	all dynamic	130 prerendered (SSG)
Dependencies	61	22

Changes

Images — enabled the optimizer in next.config.mjs (dropped unoptimized, migrated the deprecated domains key to remotePatterns, added AVIF/WebP and a 31-day minimumCacheTTL since the source is ~21 MP). Converted all four wallpaper CSS backgrounds to <Image fill>, added the missing sizes to the event banner, and set fetchPriority="high" on each hero — priority alone emits the preload link but not the attribute Lighthouse's LCP-discovery audit actually checks (priorityHinted: false was the failing item).

object-cover reproduces bg-cover geometry exactly, so ScrollLogo's hex-alignment math is untouched.

Accessibility — three concrete failures:

• Mobile menu button had no accessible name → aria-label (new nav.openMenu / nav.closeMenu messages in both locales), plus aria-expanded and aria-controls.
• Footer copyright was #6b7280 on #080814 = 4.11:1, under the 4.5:1 floor → text-gray-400 (~8.9:1).
• <Button><Link/></Button> rendered <a> inside <button> — invalid HTML, and the anchor was the real tap target at only 20 px tall. Switched to the asChild slot the component already supported (and which add-to-calendar-button.tsx already used).

Other — added a browserslist key to drop ~12 KiB of Array/Object/String polyfills; deleted 45 of 47 components/ui files (only button and table are reachable from any page) plus the orphaned use-mobile hook and 40 unused dependencies — Tailwind scans components/**, so these fed the 88 %-unused render-blocking stylesheet; added setRequestLocale so locale routes prerender.

Notes for the reviewer

• setRequestLocale only half-delivers its goal. Pages now prerender at build time, but HTML responses still carry Cache-Control: no-store because the next-intl middleware sets NEXT_LOCALE on every response. I tested localeDetection: false — it does not fix this — so this is a server-compute win, not a CDN-caching one. Removing it would mean redesigning the i18n middleware; out of scope here.
• The SEO 92 → 100 fix is not in this PR. It's a Vercel domain change: the site is served at www.cppserbia.org but every baseUrl in the code says the apex, so rel=canonical points at a redirecting host. Flipping the primary domain to cppserbia.org fixes it with no code change.
• The lockfile was regenerated with pnpm 10 so it stays lockfileVersion: '9.0' and remains readable by CI's pinned pnpm 9.
• Cloudflare is injecting a render-blocking email-decode.min.js (451 ms in the report). That's the Scrape Shield → Email Address Obfuscation toggle, not a code change.

Verification

typecheck, lint, format:check, spell, 1018 tests, and a production build all pass. Browser-checked at 412×915 that the hero renders, ScrollLogo still lands in the hexagon while scrolling, the mobile menu toggles, all CTAs navigate, and the sr-script cookie still flips /sr to Latin. The cold /_next/image transform of the 21 MP source returns 200 in ~1.3 s (no timeout), and R2 event banners optimize too (148,990 → 17,528 B).

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Project	Deployment	Actions	Updated (UTC)
cppserbia-org-website	Ready	Preview, v0	Aug 19, 2026 11:53am