feat: Phase 3 campaign management

Campaign CRUD API with cascading delete across all campaign-scoped
tables, a systems endpoint to seed the create-campaign form, active
campaign state wired to the sidebar chaos factor, and a campaign
management view for creating/switching/deleting campaigns.

public/css/styles.css

@@ -156,6 +156,22 @@ h1, h2, h3, h4, h5, h6 {
   transform: rotate(180deg);
 }
 
+.sidebar-active-campaign {
+  flex-shrink: 0;
+  padding: 10px 16px;
+  border-bottom: 1px solid var(--border);
+  font-family: var(--font-body);
+  font-size: 0.78rem;
+  color: var(--accent);
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.sidebar.collapsed .sidebar-active-campaign {
+  display: none;
+}
+
 .sidebar-nav {
   flex: 1;
   overflow-y: auto;