Recipe: Add a feature flag

1. Add an entry to KNOWN_FLAGS in lib/flags.ts:

   {
     key: "new-thing",
     description: "What flipping this off/on actually does.",
     defaultValue: false,
   }

2. Check it wherever the behavior branches — a Server Component page or layout:

   import { getFlag } from "@/lib/flags";
    
   const newThingEnabled = await getFlag("new-thing", false);

   getFlag is cache()-wrapped, so checking the same key from both a layout and the page it wraps only costs one query per request.
3. That's it — /admin/flags picks up the new entry automatically (it renders one toggle per KNOWN_FLAGS item, reading each one's current value with getFlag).
4. Verify: npm run build, then in the browser toggle the new flag at /admin/flags and confirm the row updates in place (no reload needed — setFlag calls revalidatePath("/admin/flags")), then confirm the behavior actually changed on the page(s) that check it.