fix: move all CORS headers into nginx location block

Server-level add_header does not reliably attach to proxied upstream
responses. Moving all CORS directives inside location / ensures they
are present on every response ChromaDB sends back, including 4xx/5xx.

Also removes the redundant CHROMA_SERVER_CORS_ALLOW_ORIGINS from the
chroma service so only Nginx manages CORS, avoiding conflicting
duplicate headers.

nginx.conf

@@ -7,14 +7,14 @@ http {
         listen 8666;
         server_name localhost;
 
-        # Global CORS headers for all responses
-        add_header 'Access-Control-Allow-Origin' '*' always;
-        add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS' always;
-        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization' always;
-        add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' always;
-
         location / {
-            # Handle preflight OPTIONS
+            # CORS headers for every response (including 4xx/5xx from upstream)
+            add_header 'Access-Control-Allow-Origin' '*' always;
+            add_header 'Access-Control-Allow-Methods' 'GET, POST, PUT, DELETE, OPTIONS' always;
+            add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization' always;
+            add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' always;
+
+            # Preflight OPTIONS
             if ($request_method = 'OPTIONS') {
                 add_header 'Access-Control-Max-Age' 1728000;
                 add_header 'Content-Type' 'text/plain; charset=utf-8';
@@ -29,7 +29,6 @@ http {
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
             proxy_set_header X-Forwarded-Proto $scheme;
 
-            # Support streaming
             proxy_buffering off;
             proxy_cache off;
             proxy_read_timeout 86400s;