feat: workspace-first UI refresh - PR-2 workspace detail page

- Add workspace detail page (/workspaces/:id) with 4 tabs:
  - Files: file tree, viewer, editor, git toolbar (commit/push/pull/fetch)
  - Git: branch selector, commit history
  - Tools: instance grid, start tool modal
  - Settings: workspace info read-only
- Add workspace API clients: workspace-files, workspace-git, workspace-instances
- Add hooks: useWorkspaceFiles, useWorkspaceGit, useWorkspaceInstances
- WorkspaceCard links to detail page via router Link
- Add comprehensive CSS for workspace detail layout
- Mobile: bottom tab bar, responsive file tree/split
- TypeScript + eslint clean

Quality gates: tsc --noEmit clean, eslint clean

apps/web/src/api/workspace-files.ts

@@ -0,0 +1,45 @@
+/** Workspace file API client. */
+
+import { apiClient } from "./client";
+
+export interface FileEntry {
+	name: string;
+	path: string;
+	type: "file" | "directory";
+	size?: number;
+}
+
+export async function listWorkspaceFiles(
+	workspaceId: string,
+	path: string = "",
+): Promise<FileEntry[]> {
+	const response = await apiClient.get<{ entries: FileEntry[] }>(
+		`/workspaces/${workspaceId}/files/`,
+		{ params: { path } },
+	);
+	return response.data.entries;
+}
+
+export async function getWorkspaceFileContent(
+	workspaceId: string,
+	path: string,
+): Promise<string> {
+	const response = await apiClient.get<{ content: string }>(
+		`/workspaces/${workspaceId}/files/content`,
+		{ params: { path } },
+	);
+	return response.data.content;
+}
+
+export async function saveWorkspaceFile(
+	workspaceId: string,
+	path: string,
+	content: string,
+	commitMessage?: string,
+): Promise<void> {
+	await apiClient.post(`/workspaces/${workspaceId}/files/content`, {
+		path,
+		content,
+		message: commitMessage,
+	});
+}