fix(openclaw): emit empty configSchema in plugin manifests

OpenClaw rejects generated plugin manifests that omit configSchema, even for tool plugins with no user configuration. Always emit an empty object schema so converted installs boot cleanly.\n\nAdd converter and writer regression coverage for the manifest shape.\n\nFixes #224

tests/openclaw-converter.test.ts

@@ -108,6 +108,10 @@ describe("convertClaudeToOpenClaw", () => {
     expect(bundle.manifest.id).toBe("compound-engineering")
     expect(bundle.manifest.name).toBe("Compound Engineering")
     expect(bundle.manifest.kind).toBe("tool")
+    expect(bundle.manifest.configSchema).toEqual({
+      type: "object",
+      properties: {},
+    })
     expect(bundle.manifest.skills).toContain("skills/agent-security-reviewer")
     expect(bundle.manifest.skills).toContain("skills/cmd-workflows:plan")
     expect(bundle.manifest.skills).toContain("skills/existing-skill")