Open early access copy: invites rolling out, roadmap reframed (#17)

* Update vite to 6.4.2

The Vite dependency has been updated to version 6.4.2 to incorporate recent
improvements and bug fixes. This change affects the `@tailwindcss/vite` and
`vitefu` packages.

* Upgrade Astro from 5.18.0 to 6.2.1

No source changes required: codebase uses no removed APIs
(Astro.glob, ViewTransitions, emitESMImage, astro:schema,
legacy.collections), no content collections, no Zod schemas,
no adapters. Build and dev server verified on v6.2.1.

* Update waitlist copy and CTA

Replaces "Notify Me" with "Join the Waitlist" in the signup form. Also updates
the copy for early access on the index and use case pages to reflect that early
access is open and invites are rolling out. Removes the Countdown component as
it's no longer relevant.

* Update text and footer link

Adjust wording for clarity and add a link to the Onetime Secret website in the
footer.

* Reconcile features grid with comparison table

Trim features grid to the three roadmap items shown as "Coming soon" in
the comparison (Custom Domains, Regional Storage, API & Integrations) and
reframe the section as "On the roadmap". Reorder the comparison table so
the Coming soon rows are grouped at the bottom, and drop the passphrase
row from both.

Author: delano

package.json

@@ -16,7 +16,7 @@
   },
   "dependencies": {
     "@tailwindcss/vite": "^4.2.2",
-    "astro": "^5.18.0",
+    "astro": "^6.2.1",
     "tailwindcss": "^4.2.4"
   }
 }