Add markdown event descriptions for hosts to provide context

Hosts can now add a free-form description (with markdown rendering via
goldmark) when creating or editing events. Descriptions render safely
with no raw HTML passthrough. Includes ALTER TABLE migration for
existing databases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/layout.html

@@ -97,6 +97,41 @@
     font-size: 0.78rem;
     color: #555;
   }
+  .event-description {
+    margin-top: 16px;
+    padding-top: 16px;
+    border-top: 1px solid #ddd;
+    font-size: 0.92rem;
+    line-height: 1.6;
+  }
+  .event-description h1 { font-size: 1.3rem; margin: 16px 0 8px; }
+  .event-description h2 { font-size: 1.15rem; margin: 14px 0 6px; }
+  .event-description h3 { font-size: 1.05rem; margin: 12px 0 4px; }
+  .event-description p { margin: 8px 0; }
+  .event-description ul, .event-description ol { margin: 8px 0; padding-left: 24px; }
+  .event-description li { margin: 4px 0; }
+  .event-description a { color: var(--ink); text-decoration: underline; }
+  .event-description code {
+    font-family: 'DM Mono', monospace;
+    background: var(--cream);
+    padding: 2px 6px;
+    font-size: 0.85em;
+    border: 1px solid #ddd;
+  }
+  .event-description pre {
+    background: var(--cream);
+    border: 1px solid #ddd;
+    padding: 12px;
+    overflow-x: auto;
+    margin: 8px 0;
+  }
+  .event-description pre code { background: none; border: none; padding: 0; }
+  .event-description blockquote {
+    border-left: 3px solid var(--ink);
+    padding-left: 12px;
+    margin: 8px 0;
+    color: #555;
+  }
   .section-label {
     font-family: 'DM Mono', monospace;
     font-size: 0.7rem;
@@ -230,7 +265,7 @@
     transition: box-shadow 0.1s;
     appearance: none;
   }
-  .form-row input:focus, .form-row select:focus {
+  .form-row input:focus, .form-row select:focus, .form-row textarea:focus {
     box-shadow: 3px 3px 0 var(--ink);
   }
   .btn-submit {