fix: enable folder navigation in workspace file browser

FilesTab in WorkspaceDetailPage was returning early for directories with
no action, making folders unclickable.

Changes:
- use-workspace-files.ts: add currentPath state and navigateTo() function;
  refresh() now passes currentPath to listWorkspaceFiles API
- WorkspaceDetailPage.tsx FilesTab: handleSelect now calls navigateTo()
  for directories; added navigateUp() button using '..' when not at root
- Clear selected file/editor state when changing directories

Quality gates: tsc --noEmit pass, npm run build pass, 82/82 tests pass

apps/web/src/pages/WorkspaceDetailPage.tsx

@@ -150,7 +150,7 @@ function MobileTabBar({
 /* ─── Files Tab ─── */
 
 function FilesTab({ workspaceId }: { workspaceId: string }) {
-	const { entries, content, loadFile, saveFile, loading, error } =
+	const { entries, content, currentPath, loadFile, saveFile, loading, error, navigateTo } =
 		useWorkspaceFiles(workspaceId);
 	const { status, commit, push, pull, fetch } = useWorkspaceGit(workspaceId);
 	const [selectedPath, setSelectedPath] = useState<string | null>(null);
@@ -159,13 +159,28 @@ function FilesTab({ workspaceId }: { workspaceId: string }) {
 	const [commitMessage, setCommitMessage] = useState("");
 
 	const handleSelect = (entry: FileEntry) => {
-		if (entry.type === "directory") return;
+		if (entry.type === "directory") {
+			setSelectedPath(null);
+			setIsEditing(false);
+			setEditContent(null);
+			navigateTo(entry.path);
+			return;
+		}
 		setSelectedPath(entry.path);
 		setIsEditing(false);
 		setEditContent(null);
 		loadFile(entry.path);
 	};
 
+	const navigateUp = () => {
+		if (!currentPath) return;
+		const parentPath = currentPath.split("/").slice(0, -1).join("/");
+		navigateTo(parentPath);
+		setSelectedPath(null);
+		setIsEditing(false);
+		setEditContent(null);
+	};
+
 	const handleEdit = () => {
 		if (content !== null) {
 			setEditContent(content);
@@ -224,6 +239,15 @@ function FilesTab({ workspaceId }: { workspaceId: string }) {
 			)}
 			<div className="files-split">
 				<div className="file-tree">
+					{currentPath && (
+						<button
+							className="tree-entry tree-up"
+							onClick={navigateUp}
+							type="button"
+						>
+							<Icon name="folder" size="sm" /> ..
+						</button>
+					)}
 					{loading && <p className="muted">Loading...</p>}
 					{error && <p className="error-text">{error}</p>}
 					{entries.map((entry) => (