Introduce README.md, AI-USE.md. Setup nix-shell for node. Tag personal comments with @PERSONAL-NOTE.

AI-USE.md

@@ -0,0 +1,21 @@
+Wrote most of the code by hand.
+
+My own design:
+
+- config/state/msg/update/effects, all the types
+- which hooks to use
+- remote/request/result
+- splitting the codebase into modules/folders/files
+
+LLM-generated:
+where I mostly reviewed
+
+- The Material UI / styling - after using a few components manually, I mostly let LLM decide which components to use, how to use them, and letting it decide/generate styling details.
+
+LLM-assisted:
+
+- Name suggestions
+- Project setup (linters, formatters, ts compiler settings)
+- Checking and Code Review
+- Snippet generation
+- Explanations of external API details, and confirming browser caching behaviour