fix(openclaw): remove MCP/Skills/Prompts support from OpenClaw

OpenClaw only needs provider management functionality, not MCP, Skills,
or Prompts features. This commit removes the incorrectly added support:

- Revert SCHEMA_VERSION from 6 to 5 (remove v5->v6 migration)
- Remove enabled_openclaw field from mcp_servers and skills tables
- Remove openclaw field from McpApps and SkillApps structs
- Update DAO queries to exclude enabled_openclaw column
- Fix frontend components and types to exclude openclaw from MCP/Prompts
- Update all related test files

src/components/mcp/McpFormModal.tsx

@@ -66,7 +66,6 @@ const McpFormModal: React.FC<McpFormModalProps> = ({
     codex: boolean;
     gemini: boolean;
     opencode: boolean;
-    openclaw: boolean;
   }>(() => {
     if (initialData?.apps) {
       return { ...initialData.apps };
@@ -76,7 +75,6 @@ const McpFormModal: React.FC<McpFormModalProps> = ({
       codex: defaultEnabledApps.includes("codex"),
       gemini: defaultEnabledApps.includes("gemini"),
       opencode: defaultEnabledApps.includes("opencode"),
-      openclaw: defaultEnabledApps.includes("openclaw"),
     };
   });