add duckdb-ui-client & other ts pkgs (#10)

* add duckdb-ui-client & other ts pkgs

* workflow fixes

* fix working dir

* no sparse checkout; specify package.json path

* path to pnpm-lock.yaml

* add check & build test

* workflow step descriptions

* use comments & names

* one more naming tweak

ts/tsconfig.library.json

@@ -0,0 +1,11 @@
+{
+  "extends": "./tsconfig.base.json",
+  "compilerOptions": {
+    "composite": true,
+    "declaration": true,
+    "esModuleInterop": true,
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "target": "ESNext",
+  }
+}