refactor: flatten monorepo to single web package (#12)

Flatten the pnpm monorepo (apps/web + packages/*) into a single web package at the repo root.

- Move app/lib/components/scripts/public to root; drop apps/web and packages/* wrappers
- Rewrite tsconfig paths (@infiplot/*) to ./lib/*; turbopack.root = __dirname
- Update Vercel (no root-directory) and Cloudflare (pnpm build:cf at root) deploy paths
- Regenerate pnpm-lock.yaml to drop stale workspace importers
- Bump engines.node to >=22 to match wrangler

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/ai-client/fetchWithRetry.ts

@@ -0,0 +1,39 @@
+type RetryInit = RequestInit & { retries?: number; retryDelayMs?: number };
+
+export async function fetchWithRetry(
+  url: string,
+  init: RetryInit,
+): Promise<Response> {
+  const { retries = 2, retryDelayMs = 1500, ...fetchInit } = init;
+
+  let lastError: unknown;
+  for (let attempt = 0; attempt <= retries; attempt++) {
+    try {
+      const res = await fetch(url, fetchInit);
+      if (res.ok) return res;
+      // Don't retry 4xx (client errors won't fix themselves)
+      if (res.status >= 400 && res.status < 500) return res;
+      // 5xx: retry if we have budget left
+      if (attempt < retries) {
+        await sleep(retryDelayMs * (attempt + 1));
+        continue;
+      }
+      return res;
+    } catch (err) {
+      lastError = err;
+      const isAbort =
+        err instanceof DOMException && err.name === "AbortError";
+      if (isAbort) throw err;
+      if (attempt < retries) {
+        await sleep(retryDelayMs * (attempt + 1));
+        continue;
+      }
+      throw err;
+    }
+  }
+  throw lastError;
+}
+
+function sleep(ms: number): Promise<void> {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}