fix(web): UX/a11y polish + middleware metadata route fix

- footer.tsx: Discord link → canonical discord.gg/PUwSMR9XNk
  (was outdated invite that 404'd).
- [locale]/layout.tsx: hooks count 40 → 54 (matches AGENTS.md).
- lib/stats.ts:88: drop '!' non-null assertion; use '??' fallback.
  Removes the only '!' in packages/web (project rule).
- nav-header.tsx: hamburger Button size='icon' → explicit h-11 w-11;
  mobile drawer links min-h-11 px-3 rounded-md. WCAG 2.5.5 tap
  target 44x44 minimum.
- install-command.tsx: copy button h-8 w-8 → h-11 w-11 (was 32px,
  below WCAG). Icon stays 16x16; padding fills to 44.
- middleware.ts: matcher excludes opengraph-image, twitter-image,
  icon, apple-icon, manifest.webmanifest, robots.txt, sitemap.xml.
  Previously next-intl redirected /opengraph-image → /en/opengraph-image
  breaking OG previews for crawlers that hit the unlocalized path.

packages/web/lib/stats.ts

@@ -17,6 +17,13 @@ export interface StatsData {
   weeklyDownloads: number
 }
 
+export interface FormattedStatsData {
+  readonly stars: string
+  readonly totalDownloads: string
+  readonly monthlyDownloads: string
+  readonly weeklyDownloads: string
+}
+
 let cache: StatsCache | null = null
 
 function formatCount(num: number): string {
@@ -85,7 +92,8 @@ async function fetchAllNpmDownloadsForPackage(pkg: string): Promise<number> {
   while (year <= now.getFullYear()) {
     const start = `${year}-01-01`
     const endDate = new Date(year, 11, 31)
-    const end = endDate > now ? now.toISOString().split("T")[0]! : `${year}-12-31`
+    const end =
+      endDate > now ? (now.toISOString().split("T")[0] ?? `${year}-12-31`) : `${year}-12-31`
 
     try {
       const res = await fetch(`https://api.npmjs.org/downloads/point/${start}:${end}/${pkg}`, {
@@ -129,7 +137,7 @@ export async function getStats(): Promise<StatsData> {
   return data
 }
 
-export function formatStats(stats: StatsData) {
+export function formatStats(stats: StatsData): FormattedStatsData {
   return {
     stars: formatCount(stats.stars),
     totalDownloads: formatCount(stats.totalDownloads),