bank: API for auto-created personal accounts (balance zero)

Add GET /intro/auto-account.json on the bank helper (demo-withdraw-api):
public registration with generated username/password, balance starts GOA:0,
credentials returned once for the client to display.

Nginx proxies the new path; install-demo-withdraw-api.sh installs the
location. This is separate from the shared explorer demo withdraw.

configs/bank-landing/index.html

@@ -448,6 +448,67 @@
       transform: scale(0.92);
       transform-origin: center top;
     }
+    .own-acct-lead {
+      margin: 0 0 0.85rem;
+      color: var(--muted);
+      font-size: 0.95rem;
+      line-height: 1.45;
+    }
+    .own-acct-lead strong { color: #e8c878; }
+    .own-acct-creds {
+      margin: 0 0 0.85rem;
+      padding: 0.75rem 0.85rem;
+      border-radius: 12px;
+      background: rgba(94, 234, 212, 0.08);
+      border: 1px solid rgba(94, 234, 212, 0.35);
+      text-align: left;
+    }
+    .own-acct-warn {
+      margin: 0 0 0.65rem;
+      font-size: 0.86rem;
+      color: #ccfbf1;
+      line-height: 1.4;
+    }
+    .own-acct-warn strong { color: #5eead4; }
+    .own-acct-dl {
+      margin: 0;
+      display: grid;
+      gap: 0.45rem;
+    }
+    .own-acct-dl div {
+      display: grid;
+      grid-template-columns: 5.5rem 1fr;
+      gap: 0.35rem;
+      align-items: baseline;
+    }
+    .own-acct-dl dt {
+      margin: 0;
+      font-size: 0.72rem;
+      font-weight: 700;
+      letter-spacing: 0.06em;
+      text-transform: uppercase;
+      color: var(--muted);
+    }
+    .own-acct-dl dd {
+      margin: 0;
+    }
+    .own-acct-dl code {
+      font-size: 0.95rem;
+      font-weight: 700;
+      color: #f0d090;
+      word-break: break-all;
+      user-select: all;
+    }
+    #auto-account-btn {
+      border: 0;
+      cursor: pointer;
+      width: 100%;
+      max-width: 22rem;
+    }
+    #auto-account-btn:disabled {
+      opacity: 0.55;
+      cursor: wait;
+    }
     .stats {
       background: rgba(18, 28, 28, 0.55);
       border: 1px solid rgba(62, 207, 191, 0.28);
@@ -763,18 +824,43 @@
       <div class="more-fold-body" id="more-fold-body" hidden>
         <div class="more-card">
           <h2>Own bank account?</h2>
-          <p>Register in the bank UI for your own balance (separate from the shared pool).</p>
+          <p class="own-acct-lead">
+            We can <strong>create a personal bank account for you</strong> automatically
+            (you do not pick a username or password). Balance starts at
+            <strong>GOA:0</strong> — separate from the shared pool.
+          </p>
+          <div class="more-actions" style="margin-bottom:0.75rem">
+            <button type="button" class="cta teal" id="auto-account-btn">
+              Create my bank account →
+            </button>
+          </div>
+          <div class="own-acct-creds" id="auto-account-box" hidden>
+            <p class="own-acct-warn" role="status">
+              <strong>Created for you.</strong>
+              Copy these credentials now — they are not stored for recovery.
+              Login at the bank UI; balance is <strong>GOA:0</strong>.
+            </p>
+            <dl class="own-acct-dl">
+              <div><dt>Username</dt><dd><code id="auto-account-user">—</code></dd></div>
+              <div><dt>Password</dt><dd><code id="auto-account-pass">—</code></dd></div>
+              <div><dt>Balance</dt><dd><code id="auto-account-bal">GOA:0</code></dd></div>
+            </dl>
+            <p class="meta" id="auto-account-status" style="margin:0.5rem 0 0"></p>
+          </div>
           <div class="more-qr">
             <div class="qr-taler-wrap">
               <div class="goa-pay-taler-qr" id="qr-webui-wrap">
                 <div class="goa-pay-taler-qr__inner" id="qr-webui"></div>
                 <img class="goa-pay-taler-qr__logo" id="qr-webui-logo" alt="" />
               </div>
-              <div class="qr-label">Bank UI · register / login</div>
+              <div class="qr-label">Bank UI · login with your credentials</div>
             </div>
           </div>
           <div class="more-actions">
-            <a class="cta-sec" href="/webui/">Open bank UI →</a>
+            <a class="cta-sec" href="/webui/" id="auto-account-webui">Open bank UI →</a>
+            <button type="button" class="cta-sec" id="auto-account-again" hidden style="margin-top:0.45rem">
+              Generate another account
+            </button>
           </div>
         </div>
 
@@ -1095,6 +1181,71 @@
         );
         webuiPainted = true;
       });
+
+      function createAutoAccount() {
+        var btn = document.getElementById("auto-account-btn");
+        var box = document.getElementById("auto-account-box");
+        var st = document.getElementById("auto-account-status");
+        var again = document.getElementById("auto-account-again");
+        if (btn) {
+          btn.disabled = true;
+          btn.textContent = "Creating account…";
+        }
+        if (st) st.textContent = "";
+        fetch("/intro/auto-account.json", { cache: "no-store" })
+          .then(function (r) {
+            if (!r.ok) throw new Error("HTTP " + r.status);
+            return r.json();
+          })
+          .then(function (d) {
+            if (!d || !d.ok) throw new Error((d && d.error) || "create failed");
+            if (box) box.hidden = false;
+            var u = document.getElementById("auto-account-user");
+            var p = document.getElementById("auto-account-pass");
+            var b = document.getElementById("auto-account-bal");
+            if (u) u.textContent = d.username || "—";
+            if (p) p.textContent = d.password || "—";
+            if (b) b.textContent = d.balance || "GOA:0";
+            if (st) {
+              st.textContent =
+                "Account created for you · save username & password · balance " +
+                (d.balance || "GOA:0");
+            }
+            if (btn) {
+              btn.hidden = true;
+              btn.disabled = false;
+              btn.textContent = "Create my bank account →";
+            }
+            if (again) again.hidden = false;
+          })
+          .catch(function (err) {
+            if (box) box.hidden = false;
+            if (st) {
+              st.textContent =
+                "Could not create account — try again. " +
+                (err && err.message ? err.message : "");
+            }
+            if (btn) {
+              btn.disabled = false;
+              btn.hidden = false;
+              btn.textContent = "Create my bank account →";
+            }
+          });
+      }
+      var btn = document.getElementById("auto-account-btn");
+      var again = document.getElementById("auto-account-again");
+      if (btn) btn.addEventListener("click", createAutoAccount);
+      if (again) {
+        again.addEventListener("click", function () {
+          var b = document.getElementById("auto-account-btn");
+          if (b) {
+            b.hidden = false;
+            b.disabled = false;
+          }
+          again.hidden = true;
+          createAutoAccount();
+        });
+      }
     })();
 
     function fmtCest(unix, fallback) {

configs/bank-landing/nginx-landing.conf

@@ -41,6 +41,14 @@ server {
         add_header Cache-Control "no-store" always;
         add_header Access-Control-Allow-Origin * always;
     }
+    # Auto-create personal bank account (credentials returned once; balance GOA:0)
+    location = /intro/auto-account.json {
+        proxy_pass http://127.0.0.1:19096/auto-account.json;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        add_header Cache-Control "no-store" always;
+        add_header Access-Control-Allow-Origin * always;
+    }
     location /intro/ {
         alias /var/www/bank-landing/;
     }