feat: simplify journal connection via WebSocket upgrade

Refactor the journal server to run over WebSockets on the existing
HTTP server instead of a separate MQTT TCP port. This removes the need
for a separate port configuration and simplifies the connection flow
by auto-connecting to the current host.

- Remove `--mqtt-port` CLI option
- Attach Aedes broker to the HTTP server via WebSocket upgrade
- Update UI to remove manual broker URL and player name inputs
- Add "Content Source" access from the sidebar
- Update JournalPanel to auto-connect to the local server

src/components/Sidebar.tsx

@@ -8,6 +8,7 @@ export interface SidebarProps {
   onClose: () => void;
   fileTree?: FileNode[];
   pathHeadings?: Record<string, TocNode[]>;
+  onDataSourceOpen?: () => void;
 }
 
 interface SidebarContentProps {
@@ -16,6 +17,7 @@ interface SidebarContentProps {
   currentPath: string;
   onClose: () => void;
   isDesktop?: boolean;
+  onDataSourceOpen?: () => void;
 }
 
 /**
@@ -37,15 +39,24 @@ const SidebarContent: Component<SidebarContentProps> = (props) => {
       <div class="p-4 border-b border-b-gray-200">
         <div class="flex items-center justify-between">
           <h2 class="text-lg font-bold text-gray-900">目录</h2>
-          <Show when={!props.isDesktop}>
+          <div class="flex items-center gap-1">
             <button
-              onClick={props.onClose}
-              class="text-gray-500 hover:text-gray-700"
-              title="关闭"
+              onClick={props.onDataSourceOpen}
+              class="text-gray-400 hover:text-gray-600 p-1 rounded hover:bg-gray-100"
+              title="Content Source"
             >
-              ✕
+              📂
             </button>
-          </Show>
+            <Show when={!props.isDesktop}>
+              <button
+                onClick={props.onClose}
+                class="text-gray-500 hover:text-gray-700"
+                title="关闭"
+              >
+                ✕
+              </button>
+            </Show>
+          </div>
         </div>
       </div>
 
@@ -121,6 +132,7 @@ export const MobileSidebar: Component<SidebarProps> = (props) => {
           pathHeadings={pathHeadings()}
           currentPath={location.pathname}
           onClose={props.onClose}
+          onDataSourceOpen={props.onDataSourceOpen}
         />
       </aside>
     </>
@@ -133,6 +145,7 @@ export const MobileSidebar: Component<SidebarProps> = (props) => {
 export const DesktopSidebar: Component<{
   fileTree?: FileNode[];
   pathHeadings?: Record<string, TocNode[]>;
+  onDataSourceOpen?: () => void;
 }> = (props) => {
   const location = useLocation();
   const [selfFileTree, setSelfFileTree] = createSignal<FileNode[]>([]);
@@ -158,6 +171,7 @@ export const DesktopSidebar: Component<{
         currentPath={location.pathname}
         onClose={() => {}}
         isDesktop
+        onDataSourceOpen={props.onDataSourceOpen}
       />
     </aside>
   );