fix: Fix css loading on direct links (#31)

This pull request introduces several improvements and fixes related to
asset handling, CSS layer ordering, and proxy compatibility for the
documentation marketplace. The main changes focus on ensuring consistent
CSS rendering, correct asset resolution when served from sub-paths, and
preventing encoding issues with proxies and gateways.

**Asset handling and CSS fixes:**

* In `scripts/build-vite.js`, the asset copy logic now rewrites
root-relative `url()` references in CSS bundles (e.g.,
`url(/fonts/...)`) to relative paths (e.g., `url(../fonts/...)`). This
ensures that CSS assets resolve correctly when the app is served from a
sub-path, such as `/knowledge-base/{slug}/_astro/`.
* Added `writeFileSync` import to support the CSS rewriting logic in the
build script.

**CSS layer ordering:**

* In `src/layouts/Base.astro`, a fix was added to declare `@layer base`
before sub-app stylesheets are slotted in. This guarantees that
Tailwind's base layer has lower priority than Starlight's content
layers, ensuring heading sizes and other styles render correctly on both
direct page loads and client-side navigation.

**Proxy and gateway compatibility:**

* In `nginx.conf`, the `gzip_proxied` directive is now set to `off` to
prevent nginx from gzip-encoding responses to proxies or gateways that
already sent `Accept-Encoding` upstream. This avoids issues where the
`Content-Encoding` header could be leaked to the browser, causing
decoding errors.
* Added a `Cache-Control: no-transform` header for `/knowledge-base/`
routes in `nginx.conf` to instruct intermediate proxies (like
FragmentGateway) not to transcode or re-encode responses, further
preventing encoding mismatches.

**Dependency updates:**

* Updated `@astrojs/check` development dependency from `^0.9.9` to
`^0.9.10` in `package.json`.

**Release notes:**

* Fix css loading on direct links

**Related:**

Closes #30

Author: oto-macenauer-absa

nginx.conf

@@ -8,7 +8,10 @@ server {
     # ── Compression ───────────────────────────────────────────────────────────
     gzip on;
     gzip_vary on;
-    gzip_proxied any;
+    # "off" prevents nginx from gzip-encoding responses to proxies/gateways that
+    # already sent Accept-Encoding upstream. FragmentGateway decompresses server-side
+    # but can leak Content-Encoding header to the browser causing ERR_CONTENT_DECODING_FAILED.
+    gzip_proxied off;
     gzip_comp_level 6;
     gzip_types
         text/css
@@ -66,6 +69,10 @@ server {
     # Strip the /knowledge-base/ prefix so files resolve from the dist root.
     location ^~ /knowledge-base/ {
         rewrite ^/knowledge-base/(.*)$ /$1 break;
+        # Tell any intermediate proxy (e.g. web-fragments FragmentGateway) not to
+        # transcode/re-encode this response. Prevents Content-Encoding header
+        # leakage when the gateway auto-decompresses but still forwards the header.
+        add_header Cache-Control "no-transform" always;
         try_files $uri $uri/index.html =404;
     }