Add OpenAPI docs, frontend, migrations, and API updates

- OpenAPI: add missing endpoints (add-from-url, subscriptions, public availability)
- OpenAPI: CalendarSubscription schema, Subscriptions tag
- Frontend app
- Migrations: count_for_availability, subscriptions_sync, user_preferences, calendar_settings
- Config, rate limit, auth, calendar, booking, ICS, availability, user service updates

Made-with: Cursor

frontend/vite.config.ts

@@ -0,0 +1,40 @@
+import { defineConfig, loadEnv } from "vite";
+import react from "@vitejs/plugin-react";
+import tailwindcss from "@tailwindcss/vite";
+
+export default defineConfig(({ mode }) => {
+  const env = loadEnv(mode, process.cwd(), "");
+  const apiUrl = env.VITE_API_URL || "http://localhost:8080";
+
+  return {
+    plugins: [react(), tailwindcss()],
+    server: {
+      port: 5173,
+      proxy: {
+        "/auth": apiUrl,
+        "/users": apiUrl,
+        "/calendars": apiUrl,
+        "/events": apiUrl,
+        "/contacts": apiUrl,
+        "/availability": apiUrl,
+        "/booking": apiUrl,
+        "/api-keys": apiUrl,
+        "/cal": apiUrl,
+        "/openapi.json": apiUrl,
+        "/docs": apiUrl,
+      },
+    },
+    build: {
+      outDir: "dist",
+      sourcemap: mode !== "production",
+      rollupOptions: {
+        output: {
+          manualChunks: {
+            vendor: ["react", "react-dom", "react-router-dom"],
+            date: ["date-fns"],
+          },
+        },
+      },
+    },
+  };
+});