Add proper API docs page, fix Stripe lazy init, update docs links

src/routes/signup.ts

@@ -25,7 +25,7 @@ router.post("/free", (req: Request, res: Response) => {
     apiKey: keyInfo.key,
     tier: "free",
     limit: "100 PDFs/month",
-    docs: "https://docfast.dev/#endpoints",
+    docs: "https://docfast.dev/docs",
     note: "Save this API key — it won't be shown again.",
   });
 });