feat: calculate 15% limit for book(s), blocking submission if over the limit

app/static/styles.css

@@ -725,3 +725,52 @@ input[type="radio"] { accent-color: var(--control-accent); }
     padding: 6px 8px;
   }
 }
+
+/* Signature validation states */
+.signature-validating {
+  border-color: #3b82f6 !important;
+  background-color: #eff6ff !important;
+}
+
+[data-theme="dark"] .signature-validating {
+  background-color: #1e3a8a !important;
+}
+
+.signature-valid {
+  border-color: #22c55e !important;
+  background-color: #f0fdf4 !important;
+}
+
+[data-theme="dark"] .signature-valid {
+  background-color: #14532d !important;
+}
+
+.signature-invalid {
+  border-color: #ef4444 !important;
+  background-color: #fef2f2 !important;
+}
+
+[data-theme="dark"] .signature-invalid {
+  background-color: #7f1d1d !important;
+}
+
+/* Threshold exceeded - entire row in red */
+.threshold-exceeded {
+  background-color: #fee2e2 !important;
+}
+
+[data-theme="dark"] .threshold-exceeded {
+  background-color: #991b1b !important;
+}
+
+.threshold-exceeded input,
+.threshold-exceeded select {
+  border-color: #ef4444 !important;
+}
+
+/* Disabled submit button styling */
+button[type="submit"]:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+  background-color: #9ca3af !important;
+}