Default signups off, improve Docker deploy, fix onboarding step UI.

Show a disabled-registration state on the register page when DISABLE_SIGNUPS is true (default), document docker-deploy.sh with git-SHA image tags, and align onboarding progress circles and labels on a shared grid.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/env.js

@@ -33,7 +33,7 @@ export const env = createEnv({
       .enum(["development", "test", "production"])
       .default("development"),
     DB_DISABLE_SSL: optionalEnvBoolean(),
-    DISABLE_SIGNUPS: optionalEnvBoolean(),
+    DISABLE_SIGNUPS: optionalEnvBoolean().default(true),
     CRON_SECRET: z.string().optional(),
     // SSO / Authentik (optional)
     AUTHENTIK_ISSUER: z.string().url().optional(),