fix(nginx): return 404 for non-existent articles/ and sections/ paths

Previously nginx try_files fell back to /index.html for any unmatched path,
which meant orphaned article variants (old slug directories) returned HTTP 200
with the homepage content. This caused ~1,150 orphaned pages to be crawlable.

Add explicit location blocks for /articles/ and /sections/ that use =404
instead of falling back to /index.html.

Dockerfile

@@ -32,7 +32,13 @@ RUN echo 'server { \
     location / { \
         try_files $uri $uri/ /index.html; \
     } \
-    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot|webp|avif)$ { \
+    location /articles/ { \
+        try_files $uri $uri/ =404; \
+    } \
+    location /sections/ { \
+        try_files $uri $uri/ =404; \
+    } \
+    location ~* \\.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot|webp|avif)$ { \
         expires 1y; \
         add_header Cache-Control "public, immutable"; \
     } \