OPS-1: Dockerfiles (net10 API + nginx frontend) + production config

- GerbilManagerWebAPI/Dockerfile: net7->net10 multi-stage; build context=repo
  root (includes ServiceDefaults); port 8080 (.NET 10 container default)
- gerbil-manager-web/Dockerfile: drop VITE_API_BASE_URL build-arg; nginx proxies
  /api/* to api:8080 (strip prefix), /scalar, /openapi/ -- one published port 80
- gerbil-manager-web/src/api/client.ts: default API_BASE_URL /api (relative),
  no hostname coupling at build time; Aspire still injects absolute LAN URL in dev
- GerbilManagerWebAPI/Program.cs: run EF Migrate() at startup always (not Dev-only)
- GerbilManager.ServiceDefaults/Extensions.cs: expose /health + /alive in all
  environments (compose healthcheck requires them in Production)

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

GerbilManagerWebAPI/Program.cs

@@ -43,12 +43,9 @@ app.MapDefaultEndpoints();
 app.MapOpenApi();
 app.MapScalarApiReference();
 
-if (app.Environment.IsDevelopment())
-{
-    // Aspire provisions an empty database in dev — bring the schema up to date.
-    using var scope = app.Services.CreateScope();
+// Apply EF migrations at startup (no-op if schema is current; safe for single-instance deploy).
+using (var scope = app.Services.CreateScope())
     scope.ServiceProvider.GetRequiredService<ApplicationContext>().Database.Migrate();
-}
 
 app.UseCors(LanCorsPolicy);