fix(web): remove turbostarter CTA popup + ship claudemesh OG image

Two visible launch-polish issues:

1. BuyCtaDialog popup was firing on an exponential backoff schedule
   (15s, 30s, 60s, …) pushing users toward turbostarter.dev/#pricing +
   Discord. Wrong product, wrong audience. Fully removed: mount point
   in [locale]/layout.tsx + the component file + localStorage keys will
   self-prune on next visit.

2. WhatsApp/Slack/Twitter link previews were pulling the TurboStarter
   boilerplate opengraph-image.png (from Jan 8). Replaced with a 1200×630
   claudemesh OG: "CLAUDEMESH" pixel wordmark left side, hero mesh
   composition (6 Claude Code terminals + pixel-crab hub + orange
   energy lattice + vaporwave grid floor) right side, "peer mesh for
   Claude Code sessions" tagline in mono beneath wordmark.

3. Default metadata description swapped from the dangling
   `common:product.description` i18n key (which rendered as the key
   itself because the key doesn't exist in our trimmed translations)
   to a hardcoded claudemesh description.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/lib/metadata.ts

@@ -49,7 +49,7 @@ export const getMetadata =
   (
     {
       title,
-      description = "common:product.description",
+      description = "Connect your Claude Code sessions to each other. Zero config. End-to-end encrypted. Peer mesh for Claude Code teams.",
       url,
       canonical,
       images = [DEFAULT_IMAGE],