fix: remove duplicate migrations, fix Dev nginx proxy target

- Remove 6 duplicate Phase 2 migration files (1776500001-0006) that
  failed on restart and blocked Phase 3 migrations from running
- Fix Dev nginx.conf proxy target from 192.168.1.14:8090 to
  gamegroup-pb:8090 (Docker internal DNS) since host port 8090 is
  not exposed (mapped as 8711:8090)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/nginx.conf

@@ -17,7 +17,7 @@ server {
 
     # SSE realtime 连接（必须在 /api/ 之前）
     location /api/realtime {
-        proxy_pass http://192.168.1.14:8090;
+        proxy_pass http://gamegroup-pb:8090;
         proxy_http_version 1.1;
         proxy_set_header Connection '';
         proxy_set_header Host $host;
@@ -33,7 +33,7 @@ server {
     # API 代理到局域网 PocketBase
     location /api/ {
         client_max_body_size 500m;
-        proxy_pass http://192.168.1.14:8090;
+        proxy_pass http://gamegroup-pb:8090;
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection 'upgrade';