Add PostHog, move Plausible to v4, and drop Sentry session replay

PostHog loads after the page is idle through a same-origin /ingest proxy and follows the signed-in Convex user. Plausible uses the per-site script through a /pa proxy, clear of Payload's /api routes. Sentry keeps errors and traces only. Pages load only the @gib/ui modules they import, and client code reads public env from publicEnv.ts so zod stays out of the browser.

packages/ui/src/index.tsx

@@ -1,20 +1,8 @@
-import { cx } from 'class-variance-authority';
-import { twMerge } from 'tailwind-merge';
-
-export const cn = (...inputs: Parameters<typeof cx>) => twMerge(cx(inputs));
-
-export const ccn = ({
-  context,
-  className,
-  on = '',
-  off = '',
-}: {
-  context: boolean;
-  className: string;
-  on: string;
-  off: string;
-}) => twMerge(className, context ? on : off);
-
+// Re-exports only. The Next app lists @gib/ui in `optimizePackageImports`,
+// which resolves each named import straight to its own module so a page that
+// uses Button never loads Chart (and Recharts). That only works while nothing
+// is declared in this file.
+export { cn, ccn } from './utils';
 export {
   Accordion,
   AccordionItem,

packages/ui/src/utils.ts

@@ -0,0 +1,16 @@
+import { cx } from 'class-variance-authority';
+import { twMerge } from 'tailwind-merge';
+
+export const cn = (...inputs: Parameters<typeof cx>) => twMerge(cx(inputs));
+
+export const ccn = ({
+  context,
+  className,
+  on = '',
+  off = '',
+}: {
+  context: boolean;
+  className: string;
+  on: string;
+  off: string;
+}) => twMerge(className, context ? on : off);