feat: Make single org setup more reliable by automatically adjusting RESERVED_SUBDOMAINS and ORGANIZATIONS_ENABLED (calcom#23448)

* feat: add build validation for SINGLE_ORG_SLUG and auto-enable organizations

- Add build-time validation to prevent SINGLE_ORG_SLUG from conflicting with RESERVED_SUBDOMAINS
- Auto-enable ORGANIZATIONS_ENABLED when SINGLE_ORG_SLUG is set
- Validation throws clear error message with list of reserved subdomains
- Follows existing environment validation patterns in next.config.js

Co-Authored-By: hariom@cal.com <hariombalhara@gmail.com>

* refactor: change SINGLE_ORG_SLUG validation from error to warning

- Replace build-crashing error with clear warning message
- Ignore RESERVED_SUBDOMAINS when SINGLE_ORG_SLUG is set since they don't make sense together
- Keep auto-enabling ORGANIZATIONS_ENABLED functionality
- Build continues successfully instead of failing

Co-Authored-By: hariom@cal.com <hariombalhara@gmail.com>

* Update next.config.js

* Update next.config.js

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: hariombalhara

apps/web/next.config.js

@@ -11,6 +11,9 @@ const {
   orgUserTypeRoutePath,
   orgUserTypeEmbedRoutePath,
 } = require("./pagesAndRewritePaths");
+
+adjustEnvVariables();
+
 if (!process.env.NEXTAUTH_SECRET) throw new Error("Please set NEXTAUTH_SECRET");
 if (!process.env.CALENDSO_ENCRYPTION_KEY) throw new Error("Please set CALENDSO_ENCRYPTION_KEY");
 const isOrganizationsEnabled =
@@ -715,4 +718,22 @@ const nextConfig = (phase) => {
   };
 };
 
+function adjustEnvVariables() {
+  if (process.env.NEXT_PUBLIC_SINGLE_ORG_SLUG) {
+    if (process.env.RESERVED_SUBDOMAINS) {
+      // It is better to ignore it completely so that accidentally if the org slug is itself in Reserved Subdomain that doesn't cause the booking pages to start giving 404s
+      console.warn(
+        `⚠️  WARNING: RESERVED_SUBDOMAINS is ignored when SINGLE_ORG_SLUG is set. Single org mode doesn't need to use reserved subdomain validation.`
+      );
+      delete process.env.RESERVED_SUBDOMAINS;
+    }
+
+    if (!process.env.ORGANIZATIONS_ENABLED) {
+      // This is basically a consent to add rewrites related to organizations. So, if single org slug mode is there, we have the consent already.
+      console.log("Auto-enabling ORGANIZATIONS_ENABLED because SINGLE_ORG_SLUG is set");
+      process.env.ORGANIZATIONS_ENABLED = "1";
+    }
+  }
+}
+
 module.exports = (phase) => plugins.reduce((acc, next) => next(acc), nextConfig(phase));