fix(basemap-style): emit absolute URLs so MapLibre worker can fetch

The previous rewrite produced relative `/api/basemap-tile/…` URLs in
the resolved style. MapLibre loads vector tiles + sprites + glyphs
inside a Web Worker, where relative URLs have no base context and
fetch() rejects them with "Failed to construct 'Request': Failed to
parse URL". Browser console filled with one such error per tile
request → empty cream map all over again.

Fix: prepend the request origin (honoring Traefik's
x-forwarded-proto / x-forwarded-host) so every rewritten URL is
absolute. Same behaviour from the main thread; Web Worker fetch
also works because it now has a parseable URL.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/api/basemap-style/[id]/route.ts

@@ -24,7 +24,7 @@ export const dynamic = "force-dynamic";
 
 const ALLOWED_STYLES = new Set(["liberty", "dark", "positron", "bright"]);
 const OFM_BASE = "https://tiles.openfreemap.org";
-const TILE_PROXY_PREFIX = "/api/basemap-tile";
+const TILE_PROXY_PATH = "/api/basemap-tile";
 
 type StyleSource = {
   type: string;
@@ -62,20 +62,31 @@ async function fetchJson<T>(url: string): Promise<T> {
 
 /** Replace `https://tiles.openfreemap.org/<rest>` with the architots
  *  proxy prefix so the browser never talks to openfreemap directly.
- *  Leaves `{z}/{x}/{y}` template tokens intact. */
-function rewriteUpstreamUrl(value: string): string {
+ *  Emits ABSOLUTE URLs — MapLibre loads tiles in a Web Worker context
+ *  where relative URLs fail to parse ("Failed to construct 'Request':
+ *  Failed to parse URL"). Leaves `{z}/{x}/{y}` template tokens intact. */
+function rewriteUpstreamUrl(value: string, origin: string): string {
   if (typeof value !== "string") return value;
   if (value.startsWith(OFM_BASE)) {
-    return `${TILE_PROXY_PREFIX}${value.slice(OFM_BASE.length)}`;
+    return `${origin}${TILE_PROXY_PATH}${value.slice(OFM_BASE.length)}`;
   }
   return value;
 }
 
 export async function GET(
-  _request: Request,
+  request: Request,
   { params }: { params: Promise<{ id: string }> },
 ) {
   const { id } = await params;
+  // Build the absolute origin used in rewritten URLs. Honor proxy
+  // headers (Traefik forwards x-forwarded-{proto,host}) so URLs match
+  // the user's external view of the site even when the Next process
+  // sees the request on its internal hostname:port.
+  const proto =
+    request.headers.get("x-forwarded-proto") ?? new URL(request.url).protocol.replace(":", "");
+  const host =
+    request.headers.get("x-forwarded-host") ?? request.headers.get("host") ?? new URL(request.url).host;
+  const origin = `${proto}://${host}`;
   if (!ALLOWED_STYLES.has(id)) {
     return NextResponse.json({ error: "unknown_style" }, { status: 404 });
   }
@@ -119,7 +130,7 @@ export async function GET(
     // that point.
     for (const source of Object.values(resolved)) {
       if (Array.isArray(source.tiles)) {
-        source.tiles = source.tiles.map(rewriteUpstreamUrl);
+        source.tiles = source.tiles.map((u) => rewriteUpstreamUrl(u, origin));
       }
     }
 
@@ -128,18 +139,21 @@ export async function GET(
     // multi-image-set styles). Handle both.
     let sprite: unknown = style.sprite;
     if (typeof sprite === "string") {
-      sprite = rewriteUpstreamUrl(sprite);
+      sprite = rewriteUpstreamUrl(sprite, origin);
     } else if (Array.isArray(sprite)) {
       sprite = sprite.map((s) =>
         s && typeof s === "object" && "url" in s
-          ? { ...s, url: rewriteUpstreamUrl(String((s as { url: unknown }).url)) }
+          ? {
+              ...s,
+              url: rewriteUpstreamUrl(String((s as { url: unknown }).url), origin),
+            }
           : s,
       );
     }
 
     const glyphs =
       typeof style.glyphs === "string"
-        ? rewriteUpstreamUrl(style.glyphs)
+        ? rewriteUpstreamUrl(style.glyphs, origin)
         : style.glyphs;
 
     return NextResponse.json(