MoonPay card on-ramp for crypto-new members (zero custody)

- GET /api/public/moonpay-url: returns a MoonPay checkout link for POL on
  Polygon (pol_polygon). With partner keys in config (moonpayPublicKey/
  moonpaySecretKey, now PATCHable), the URL is HMAC-signed and prefilled
  with the member's own wallet address + shortfall amount; without keys it
  falls back to MoonPay's generic buy page. MoonPay is merchant of record -
  the site never touches funds.
- Join page: when the connected wallet can't cover the Premium entry, a
  funding box appears with the exact shortfall, a buy button (new tab), and
  a refresh-balance button.
- Training page: "buy POL with a card" callout after the funding video with
  the three things to get right (POL, Polygon network, own address).
- Start page: one-line card-buy pointer under the sponsor card.
- Chatbot canned answer + AI system prompt updated (funding guidance).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

public/training.html

@@ -14,6 +14,8 @@
 
 <div class="video-card" style="max-width:880px;margin:0 auto 26px"><div style="padding:6px 6px 0"><div class="eyebrow">Video 3 · 3 min</div><h2 style="margin:6px 0 6px">Funding your wallet</h2><p style="color:var(--muted);margin:0 0 12px">Get POL onto Polygon Mainnet — enough for the 362 POL Premium entry plus a little extra for gas.</p></div><video class="video-frame" style="display:block;width:100%;height:auto;aspect-ratio:16/9" controls preload="metadata" poster="/training/funding_your_wallet_poster.jpg" src="/training/funding_your_wallet.mp4"></video></div>
 
+<div class="callout" style="max-width:880px;margin:0 auto 26px"><strong>💳 Brand new to crypto? You can buy POL with a card.</strong> If you don't have crypto anywhere yet, the simplest path is <a href="https://www.moonpay.com/buy/pol" target="_blank" rel="noopener nofollow">MoonPay</a> — buy with a debit/credit card, Apple Pay, or Google Pay. Three things to get right: choose <strong>POL on the Polygon network</strong>, paste <strong>your own wallet address</strong> from Video 2 as the destination, and buy about <strong>385 POL</strong> (the 362 entry plus a little gas). The crypto is delivered straight to your wallet — this site never touches your money. MoonPay handles ID verification and charges its own card fee (~4.5%); a first purchase can take a few minutes to arrive. The join page will also offer this automatically if your connected wallet is short.</div>
+
 <div class="video-card" style="max-width:880px;margin:0 auto 26px"><div style="padding:6px 6px 0"><div class="eyebrow">Video 4 · 4 min · the new way to join</div><h2 style="margin:6px 0 6px">Joining right on the site — connect wallet &amp; buy your position</h2><p style="color:var(--muted);margin:0 0 12px">The whole join process, start to finish: open your invite link (or <a href="/start" style="color:var(--teal)">the start page</a>), connect your wallet, and buy your Premium position in one guided flow — the sponsor ID is filled in for you automatically.</p></div><video class="video-frame" style="display:block;width:100%;height:auto;aspect-ratio:16/9" controls preload="metadata" poster="/training/new_integrated_join_process_poster.jpg" src="/training/new_integrated_join_process.mp4"></video></div>
 
 <div class="video-card" style="max-width:880px;margin:0 auto 26px"><div style="padding:6px 6px 0"><div class="eyebrow">Video 5 · 5 min · backup method</div><h2 style="margin:6px 0 6px">Buying the Premium position in the dApp</h2><p style="color:var(--muted);margin:0 0 12px">If the on-site wallet connect isn't an option for you, you can still join the original way: connect to the RM Circle dApp with the current team sponsor and complete your Premium entry there. Double-check the sponsor ID matches the start page before signing.</p></div><video class="video-frame" style="display:block;width:100%;height:auto;aspect-ratio:16/9" controls preload="metadata" poster="/training/buying_the_premium_position_poster.jpg" src="/training/buying_the_premium_position.mp4"></video></div>