feat(FN-1946): add slash skill autocomplete to chat input

- Fetch discovered skills per project and track autocomplete menu/filter/highlight state in ChatView
- Detect slash triggers in the composer, render filtered skill suggestions, and insert /skill:<name> on selection
- Support keyboard and focus UX for the menu (arrow navigation, Enter/Tab select, Escape dismiss, blur/focus timing)
- Add chat skill menu styling for desktop and mobile layouts using existing dashboard tokens
- Expand ChatView tests to cover menu rendering, filtering, selection flows, loading state, and fetch failures

packages/dashboard/app/styles.css

@@ -30770,6 +30770,7 @@ html .column.drag-over * {
 
 /* Input area */
 .chat-input-area {
+  position: relative;
   padding: 12px 16px;
   border-top: 1px solid var(--border);
   display: flex;
@@ -30777,6 +30778,68 @@ html .column.drag-over * {
   gap: 8px;
 }
 
+/* === Chat Skill Menu === */
+.chat-skill-menu {
+  position: absolute;
+  left: var(--space-lg);
+  bottom: calc(100% + var(--space-xs));
+  min-width: calc((var(--space-xl) * 10) + var(--space-2xl) + (var(--space-xs) * 2));
+  max-width: calc(100% - (var(--space-lg) * 2));
+  max-height: calc(var(--space-xl) * 10);
+  overflow-y: auto;
+  background: var(--surface);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-md);
+  box-shadow: var(--shadow-lg);
+  z-index: 50;
+}
+
+.chat-skill-menu-item {
+  width: 100%;
+  border: none;
+  background: transparent;
+  color: inherit;
+  text-align: left;
+  padding: var(--space-sm) var(--space-md);
+  cursor: pointer;
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-xs);
+  transition: background var(--transition-fast);
+}
+
+.chat-skill-menu-item:hover,
+.chat-skill-menu-item--highlighted {
+  background: var(--card-hover);
+}
+
+.chat-skill-menu-item:focus-visible {
+  outline: none;
+  box-shadow: var(--focus-ring-strong);
+  background: var(--card-hover);
+}
+
+.chat-skill-menu-item-name {
+  font-size: 0.8125rem;
+  color: var(--text);
+  font-family: var(--font-mono);
+}
+
+.chat-skill-menu-item-description {
+  font-size: 0.75rem;
+  color: var(--text-muted);
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  max-width: calc((var(--space-xl) * 10) + var(--space-lg) + var(--space-xs));
+}
+
+.chat-skill-menu-empty {
+  padding: var(--space-sm) var(--space-md);
+  color: var(--text-muted);
+  font-size: 0.8125rem;
+}
+
 .chat-input-textarea {
   flex: 1;
   resize: none;
@@ -32746,6 +32809,13 @@ html .column.drag-over * {
   .chat-thread-header {
     padding: 8px 12px;
   }
+
+  .chat-skill-menu {
+    left: var(--space-md);
+    right: calc(var(--space-md) + var(--mobile-nav-height));
+    min-width: 0;
+    max-width: none;
+  }
 }
 
 /* === Task Documents === */