feat: add repository workspace as default project view

- Create git file utilities (list_tree, get_file_content, list_branches, commit_file)
- Add file browsing API endpoints (list, content, branches, update)
- Create RepoWorkspace page with sidebar + main content layout
- Add FileTree component with directory navigation
- Add FileViewer component for viewing file contents
- Update project list to link to workspace
- Add workspace CSS styles
- Update router with workspace route

Quality gates: ruff ✓, mypy ✓, typecheck ✓, build ✓

apps/web/src/router.tsx

@@ -8,6 +8,7 @@ import { ProfilePage } from "./pages/profile";
 import { ProjectsPage } from "./pages/projects";
 import { GitRepositoriesPage } from "./pages/git-repositories";
 import { GitHistoryPage } from "./pages/git-history";
+import { RepoWorkspace } from "./pages/repo-workspace";
 import { SSHKeysPage } from "./pages/ssh-keys";
 import { SettingsPage } from "./pages/settings";
 import { ToolTypesPage } from "./pages/tool-types";
@@ -26,6 +27,7 @@ export const AppRouter = () => {
       >
         <Route index element={<DashboardPage />} />
         <Route path="projects" element={<ProjectsPage />} />
+        <Route path="projects/:projectId" element={<RepoWorkspace />} />
         <Route path="projects/:projectId/repositories" element={<GitRepositoriesPage />} />
         <Route path="projects/:projectId/repositories/:repoId/history" element={<GitHistoryPage />} />
         <Route path="ssh-keys" element={<SSHKeysPage />} />