Replace flat sub-tab bars with tree sidebar navigation

Add TreeNav component that groups related entity types into a
collapsible hierarchy for Targets and Sources tabs. Targets tree
shows section-level leaves (Devices, Color Strips, LED Targets,
KC Targets, Pattern Templates) with scroll-to-section on click.
Sources tree groups into Picture, Audio, and Utility categories.

Also fixes missing csAudioTemplates in stream section expand/collapse.

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

server/src/wled_controller/static/css/streams.css

@@ -700,6 +700,7 @@ body.pp-filter-dragging .pp-filter-drag-handle {
 /* Sub-tab content sections */
 .subtab-section {
     margin-bottom: 24px;
+    scroll-margin-top: var(--header-height, 48px);
 }
 
 .subtab-section:last-child {

server/src/wled_controller/static/css/tree-nav.css

@@ -0,0 +1,255 @@
+/* ===========================
+   Tree Sidebar Navigation
+   =========================== */
+
+.tree-layout {
+    display: flex;
+    gap: 20px;
+    align-items: flex-start;
+}
+
+.tree-sidebar {
+    width: 210px;
+    min-width: 210px;
+    flex-shrink: 0;
+    position: sticky;
+    top: calc(var(--header-height, 48px) + 52px);
+    max-height: calc(100vh - var(--header-height, 48px) - 80px);
+    overflow-y: auto;
+    padding: 4px 0;
+}
+
+.tree-content {
+    flex: 1;
+    min-width: 0;
+}
+
+/* ── Group ── */
+
+.tree-group {
+    margin-bottom: 2px;
+}
+
+.tree-group-header {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 6px 10px;
+    cursor: pointer;
+    user-select: none;
+    font-size: 0.78rem;
+    font-weight: 600;
+    color: var(--text-secondary);
+    border-radius: 6px;
+    transition: color 0.15s, background 0.15s;
+    text-transform: uppercase;
+    letter-spacing: 0.03em;
+}
+
+.tree-group-header:hover {
+    color: var(--text-color);
+    background: var(--bg-secondary);
+}
+
+.tree-chevron {
+    font-size: 0.5rem;
+    width: 10px;
+    display: inline-block;
+    flex-shrink: 0;
+    transition: transform 0.2s ease;
+    color: var(--text-secondary);
+}
+
+.tree-chevron.open {
+    transform: rotate(90deg);
+}
+
+.tree-node-icon {
+    flex-shrink: 0;
+    line-height: 1;
+}
+
+.tree-node-icon .icon {
+    width: 14px;
+    height: 14px;
+}
+
+.tree-node-title {
+    flex: 1;
+    min-width: 0;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+}
+
+.tree-group-count {
+    background: var(--border-color);
+    color: var(--text-secondary);
+    font-size: 0.6rem;
+    font-weight: 600;
+    padding: 0 5px;
+    border-radius: 8px;
+    flex-shrink: 0;
+    min-width: 16px;
+    text-align: center;
+}
+
+/* ── Children (leaves) ── */
+
+.tree-children {
+    overflow: hidden;
+}
+
+.tree-children.collapsed {
+    display: none;
+}
+
+.tree-leaf {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 5px 10px 5px 26px;
+    cursor: pointer;
+    font-size: 0.8rem;
+    color: var(--text-secondary);
+    border-radius: 6px;
+    margin: 1px 0;
+    transition: color 0.15s, background 0.15s;
+}
+
+.tree-leaf:hover {
+    color: var(--text-color);
+    background: var(--bg-secondary);
+}
+
+.tree-leaf.active {
+    color: var(--primary-text-color);
+    background: color-mix(in srgb, var(--primary-color) 12%, transparent);
+    font-weight: 600;
+}
+
+.tree-leaf.active .tree-count {
+    background: var(--primary-color);
+    color: var(--primary-contrast);
+}
+
+/* ── Standalone leaf (top-level, no group) ── */
+
+.tree-standalone {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 6px 10px;
+    cursor: pointer;
+    font-size: 0.8rem;
+    font-weight: 500;
+    color: var(--text-secondary);
+    border-radius: 6px;
+    margin: 1px 0;
+    transition: color 0.15s, background 0.15s;
+}
+
+.tree-standalone:hover {
+    color: var(--text-color);
+    background: var(--bg-secondary);
+}
+
+.tree-standalone.active {
+    color: var(--primary-text-color);
+    background: color-mix(in srgb, var(--primary-color) 12%, transparent);
+    font-weight: 600;
+}
+
+.tree-standalone.active .tree-count {
+    background: var(--primary-color);
+    color: var(--primary-contrast);
+}
+
+/* ── Count badge ── */
+
+.tree-count {
+    background: var(--border-color);
+    color: var(--text-secondary);
+    font-size: 0.6rem;
+    font-weight: 600;
+    padding: 0 5px;
+    border-radius: 8px;
+    flex-shrink: 0;
+    min-width: 16px;
+    text-align: center;
+}
+
+/* ── Extra (expand/collapse, tutorial buttons) ── */
+
+.tree-extra {
+    padding: 8px 10px;
+    margin-top: 4px;
+    border-top: 1px solid var(--border-color);
+    display: flex;
+    gap: 4px;
+    align-items: center;
+}
+
+/* ── Responsive: stack on narrow screens ── */
+
+@media (max-width: 900px) {
+    .tree-layout {
+        flex-direction: column;
+        gap: 0;
+    }
+
+    .tree-sidebar {
+        width: 100%;
+        min-width: unset;
+        position: static;
+        max-height: none;
+        overflow-y: visible;
+        padding: 0 0 8px 0;
+        margin-bottom: 8px;
+        border-bottom: 1px solid var(--border-color);
+        display: flex;
+        flex-wrap: wrap;
+        align-items: center;
+        gap: 2px;
+    }
+
+    .tree-group {
+        display: flex;
+        align-items: center;
+        flex-wrap: wrap;
+        gap: 2px;
+        margin-bottom: 0;
+    }
+
+    .tree-group-header {
+        padding: 4px 8px;
+        text-transform: none;
+        letter-spacing: normal;
+    }
+
+    .tree-children {
+        display: flex;
+        flex-wrap: wrap;
+        gap: 2px;
+    }
+
+    .tree-children.collapsed {
+        display: none;
+    }
+
+    .tree-leaf {
+        padding: 4px 10px;
+        margin: 0;
+    }
+
+    .tree-standalone {
+        padding: 4px 10px;
+    }
+
+    .tree-extra {
+        margin-top: 0;
+        border-top: none;
+        padding: 4px;
+        margin-left: auto;
+    }
+}