Fix stale favicon: version icon URLs and stop immutable-caching brand assets

The old favicon/logo were pinned by `Cache-Control: immutable` (1 year), so
browsers never refetched the new glass-bloom mark.
- _headers: favicon.ico + icon.png now cache for a day (revalidating), not
  immutable; drop dead /screenshots + /assets rules; cache /images for a week
- version icon references (?v=2) so existing immutable caches are busted now
- add a modern PNG icon link (/icon.png) that browsers prefer over the .ico
- remove the dead root _headers duplicate (only public/_headers ships)

landing/_headers

@@ -1,21 +0,0 @@
-/*
-  Content-Security-Policy: default-src 'self'; script-src 'self' 'unsafe-inline' https://static.cloudflareinsights.com; style-src 'self' 'unsafe-inline'; font-src 'self' data:; img-src 'self' data:; connect-src 'self' https://cloudflareinsights.com; base-uri 'self'; form-action 'self'; frame-ancestors 'none'
-  Permissions-Policy: camera=(), microphone=(), geolocation=()
-  Referrer-Policy: strict-origin-when-cross-origin
-  X-Content-Type-Options: nosniff
-  X-Frame-Options: DENY
-
-/screenshots/*
-  Cache-Control: public, max-age=31536000, immutable
-
-/assets/*
-  Cache-Control: public, max-age=31536000, immutable
-
-/_next/static/*
-  Cache-Control: public, max-age=31536000, immutable
-
-/favicon.ico
-  Cache-Control: public, max-age=31536000, immutable
-
-/icon.png
-  Cache-Control: public, max-age=31536000, immutable

landing/app/layout.tsx

@@ -93,8 +93,11 @@ export const metadata: Metadata = {
     follow: true,
   },
   icons: {
-    icon: "/favicon.ico",
-    apple: "/icon.png",
+    icon: [
+      { url: "/favicon.ico?v=2", sizes: "any", type: "image/x-icon" },
+      { url: "/icon.png?v=2", type: "image/png" },
+    ],
+    apple: "/icon.png?v=2",
   },
 };
 

landing/components/brand/icon-mark.tsx

@@ -2,7 +2,7 @@
 export function IconMark({ size = 32 }: { size?: number }) {
   return (
     <img
-      src="/icon.png"
+      src="/icon.png?v=2"
       alt=""
       aria-hidden="true"
       width={size}

landing/public/_headers

@@ -5,17 +5,14 @@
   X-Content-Type-Options: nosniff
   X-Frame-Options: DENY
 
-/screenshots/*
-  Cache-Control: public, max-age=31536000, immutable
-
-/assets/*
-  Cache-Control: public, max-age=31536000, immutable
-
 /_next/static/*
   Cache-Control: public, max-age=31536000, immutable
 
+/images/*
+  Cache-Control: public, max-age=604800
+
 /favicon.ico
-  Cache-Control: public, max-age=31536000, immutable
+  Cache-Control: public, max-age=86400
 
 /icon.png
-  Cache-Control: public, max-age=31536000, immutable
+  Cache-Control: public, max-age=86400