Project updates from Template

This commit contains the latest updates from the generic Website template, which rework the compression and localization:

- Reworked the compression and localization in the Infrastructure package. (3c568e4)
- Adopted the reworked compression and localization in the Website service. (08cf3e3)

The template commit that only touched the root README (53676ed) was left out, as this project no longer carries that file.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Services/Website/Sources/Library/Public/Controllers/RootController.swift

@@ -1,6 +1,7 @@
 import Foundation
 import Hummingbird
 import Infrastructure
+import Localization
 
 /// Serves the website's root routes.
 ///
@@ -13,10 +14,13 @@ import Infrastructure
 /// ```
 ///
 /// - Note: `Context` is the request context the routes are resolved against, and must match the context of the router the routes are added to.
-public struct RootController<Context: LocalizedRequestContext> {
+public struct RootController<Context: RequestContext> {
 
     // MARK: Properties
 
+    /// Negotiates the language the bare route answers in.
+    private let negotiate: Negotiate
+
     /// The landing page, rendered once per supported language and reused for every request.
     private let responses: LocalizedHTMLCollectionResponse
 
@@ -32,7 +36,13 @@ public struct RootController<Context: LocalizedRequestContext> {
         siteOrigin: String? = nil,
         analytics: Analytics? = nil
     ) {
-        self.responses = .init(bundle: .module) {
+        self.negotiate = .init(bundle: .module)
+        // The bare route negotiates, so the pages declare `Vary: Accept-Language`; the prefixed editions share the cache
+        // and carry it too.
+        self.responses = .init(
+            bundle: .module,
+            variesOnAcceptLanguage: true
+        ) {
             IndexPage(
                 locale: $0,
                 assetVersion: assetVersion,
@@ -80,26 +90,27 @@ private extension RootController {
 
     /// Handles a request for the landing page.
     ///
-    /// Renders the ``IndexPage`` in the language stored on the context by ``LocalizationMiddleware``, falling back to the default language.
+    /// Renders the ``IndexPage`` in the language negotiated from the request — its `lang` query parameter, then the leading path segment, then
+    /// `Accept-Language` — falling back to the default language.
     /// - Parameters:
     ///   - request: the incoming request.
     ///   - context: the context the request is resolved against.
-    /// - Returns: the cached ``IndexPage`` response for the context's language.
+    /// - Returns: the cached ``IndexPage`` response for the negotiated language.
     @Sendable
     func index(
         request: Request,
         context: Context
     ) -> Response {
         responses.response(
-            for: context.language,
+            for: negotiate(for: request),
             request: request
         )
     }
 
     /// Builds the handler serving the landing page in one fixed language, for the routes carrying the language in their path.
     ///
-    /// The path *is* the language choice, so the negotiated context language is ignored: a prefixed URL answers in its language for every
-    /// visitor and every crawler alike, which is what lets a search engine index it as that edition.
+    /// The path *is* the language choice, so nothing is negotiated: a prefixed URL answers in its language for every visitor and every crawler
+    /// alike, which is what lets a search engine index it as that edition.
     /// - Parameter language: the language the route serves.
     /// - Returns: the handler answering requests for that edition of the page.
     func index(