Add production KV store validation to Lightning payment verification endpoints

[Copilot]

The Lightning payment verification endpoints were falling back to in-memory storage when the GATED_CONTENT KV binding was missing in production, causing intermittent failures across Cloudflare Workers isolates.

Changes

• Added explicit KV binding validation in /api/genesis/verify-lightning-payment and /api/membership/verify-lightning-payment
• Returns 503 Service Unavailable when KV binding is absent in production environments
• Matches existing pattern in /api/membership/strike-webhook

const kv = platform?.env?.GATED_CONTENT ?? null;
if (!kv && env.NODE_ENV === 'production') {
  return json(
    {
      error: 'Service unavailable',
      message: 'GATED_CONTENT KV namespace is not configured'
    },
    { status: 503 }
  );
}

This makes configuration errors explicit rather than silently degrading to unreliable in-memory state.

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[cloudflare-workers-and-pages]

Deploying frontend with    Cloudflare Pages

Latest commit:	202ee08
Status:	⚡️  Build in progress...

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