refactor(phase3): remove OpenClaw compatibility layer

Phase 3 Configuration Migration completed:
- Remove OpenClaw backend type selector from General.tsx
- Update default workspace path from ~/.openclaw to ~/.openfang
- Update default port from 18789 to 50051
- Archive openclaw.default.json to docs/archive/openclaw-legacy/
- Remove OpenClaw migration UI from Workspace settings
- Update About.tsx to reference OpenFang
- Clean up gateway-client.ts comments

All OpenClaw compatibility code removed. ZCLAW now exclusively
targets OpenFang (Rust Agent OS) backend.

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

desktop/src/components/RightPanel.tsx

@@ -209,7 +209,7 @@ export function RightPanel() {
                       ))}
                     </div>
                   </div>
-                  <AgentRow label="工作目录" value={selectedClone?.workspaceDir || workspaceInfo?.path || '~/.openclaw/zclaw-workspace'} />
+                  <AgentRow label="工作目录" value={selectedClone?.workspaceDir || workspaceInfo?.path || '~/.openfang/zclaw-workspace'} />
                   <AgentRow label="解析目录" value={selectedClone?.workspaceResolvedPath || workspaceInfo?.resolvedPath || '-'} />
                   <AgentRow label="文件限制" value={selectedClone?.restrictFiles ? '已开启' : '未开启'} />
                   <AgentRow label="优化计划" value={selectedClone?.privacyOptIn ? '已加入' : '未加入'} />
@@ -546,7 +546,7 @@ function createAgentDraft(
     nickname: clone.nickname || '',
     model: clone.model || currentModel,
     scenarios: clone.scenarios?.join(', ') || '',
-    workspaceDir: clone.workspaceDir || '~/.openclaw/zclaw-workspace',
+    workspaceDir: clone.workspaceDir || '~/.openfang/zclaw-workspace',
     userName: clone.userName || '',
     userRole: clone.userRole || '',
     restrictFiles: clone.restrictFiles ?? true,