feat(14.2.1-01): add optional surf LocaleResolver seam

Look up a backpack-published resolver so a compiled translate plugin can
strip an enabled URL prefix and write a validated locale onto context.

Co-authored-by: Cursor <cursoragent@cursor.com>

modules/surf/locale_resolver.go

@@ -0,0 +1,15 @@
+package surf
+
+import "net/http"
+
+// LocaleResolver is an optional backpack-published service that selects a
+// validated locale code for a request. When none is published, surf keeps
+// writing the raw Accept-Language header onto the request context.
+type LocaleResolver interface {
+	// Resolve returns a validated locale code for r. It may set cookies on w
+	// and must not store request locale on a process-wide variable.
+	Resolve(w http.ResponseWriter, r *http.Request) string
+	// Rewrite returns a request whose URL has a valid enabled locale prefix
+	// stripped so routing sees the unprefixed path, or r unchanged.
+	Rewrite(r *http.Request) *http.Request
+}