feat(FN-3806): implement rooms create modal and chat sidebar with plugin ro

Adds a rooms feature to the chat sidebar including a new CreateRoomModal for creating chat rooms, with mobile selection handling and search empty-state copy fixes. Also introduces listTasksModifiedSince plugin contract and report plugin scaffold, replacing the removed dashboard roadmap backend.

Fusion-Task-Id: FN-3806

packages/dashboard/app/components/ChatView.css

@@ -83,6 +83,18 @@
   box-shadow: inset 0 calc(var(--btn-border-width) * -2) 0 var(--todo);
 }
 
+.chat-sidebar-rooms {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+}
+
+.chat-sidebar-rooms-header {
+  padding: var(--space-sm) var(--space-md);
+  border-bottom: 1px solid var(--border);
+}
+
 .chat-sidebar-rooms-empty {
   flex: 1;
   display: flex;
@@ -94,6 +106,59 @@
   font-size: var(--space-md);
 }
 
+.chat-room-item {
+  width: 100%;
+  display: flex;
+  flex-direction: column;
+  align-items: flex-start;
+  gap: var(--space-xs);
+  border: none;
+  border-radius: var(--radius-md);
+  background: transparent;
+  color: var(--text);
+  padding: var(--space-sm) var(--space-md);
+  text-align: left;
+}
+
+.chat-room-item:hover {
+  background: var(--card-hover);
+}
+
+.chat-room-item:focus-visible {
+  outline: none;
+  box-shadow: var(--focus-ring-strong);
+}
+
+.chat-room-item--active {
+  background: color-mix(in srgb, var(--todo) 12%, transparent);
+}
+
+.chat-room-item-name {
+  font-weight: 500;
+}
+
+.chat-room-item-meta {
+  color: var(--text-muted);
+  font-size: var(--space-sm);
+}
+
+.chat-thread--rooms-placeholder {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-sm);
+  justify-content: center;
+  align-items: center;
+}
+
+.chat-rooms-placeholder-title {
+  color: var(--text);
+  font-weight: 600;
+}
+
+.chat-rooms-placeholder-copy {
+  color: var(--text-muted);
+}
+
 .chat-sidebar-search-wrapper {
   position: relative;
   display: flex;
@@ -1312,4 +1377,14 @@
   .chat-jump-to-latest {
     bottom: calc(var(--space-xl) * 4);
   }
+
+  .chat-sidebar-rooms-header .btn {
+    width: 100%;
+    justify-content: center;
+  }
+
+  .chat-thread--rooms-placeholder {
+    padding: var(--space-lg);
+    text-align: center;
+  }
 }