docs: per-tenant frontend deploy paths in runbook

Ramaiah and Global now have separate frontend dirs on EC2
(frontend-ramaiah, frontend-global) with tenant-specific VITE_API_URL
baked at build time. Also updated api-client.ts to fallback to
window.location.origin when VITE_API_URL is empty.

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

src/lib/api-client.ts

@@ -1,6 +1,9 @@
 import { notify } from './toast';
 
-const API_URL = import.meta.env.VITE_API_URL ?? 'http://localhost:4100';
+// In production, use the current origin — Caddy routes /api/* to the
+// correct per-tenant sidecar based on hostname. Only use VITE_API_URL
+// for local dev (pointing to a specific sidecar).
+const API_URL = import.meta.env.VITE_API_URL || window.location.origin;
 
 class AuthError extends Error {
     constructor(message = 'Authentication required') {