fix: use base URL for Supabase client, nginx proxies /rest/v1/ and /auth/v1/

The Supabase JS client auto-derives API paths from the base URL:
- REST: ${url}/rest/v1/
- Auth: ${url}/auth/v1/

Nginx now proxies these standard paths to the correct backend services.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nginx.conf

@@ -10,8 +10,8 @@ server {
         try_files $uri $uri/ /index.html;
     }
 
-    # Reverse proxy: PostgREST (database REST API)
-    location /rest/ {
+    # Reverse proxy: PostgREST (Supabase client hits /rest/v1/*)
+    location /rest/v1/ {
         proxy_pass http://rest:3000/;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
@@ -19,8 +19,8 @@ server {
         proxy_set_header X-Forwarded-Proto $scheme;
     }
 
-    # Reverse proxy: GoTrue (auth)
-    location /auth/ {
+    # Reverse proxy: GoTrue auth (Supabase client hits /auth/v1/*)
+    location /auth/v1/ {
         proxy_pass http://auth:9999/;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;