Add codegen-llm: LLM-based Pydantic type generation from River TypeScript servers

TypeScript CLI tool that uses the Codex SDK to generate clean, well-structured
Pydantic v2 models from a River TypeScript server's source code. Instead of the
current mechanical codegen that produces awful names and duplicated types, this
points a Codex agent at the TypeScript source so it can read how types are named
and organised, then generates matching Python models.

Key features:
- Reads TypeScript TypeBox definitions to mirror naming and composition
- Generates shared/reusable types (common errors, domain types)
- Verifies correctness by comparing generated JSON schemas against the
  serialised River schema (via a Python verification script)
- Iterates on failures: feeds verification errors back to the model
- Exposed as a CLI for GitHub Actions integration

Usage:
  codegen-llm generate \
    --server-src ./path/to/ts/services \
    --schema ./schema.json \
    --output ./generated \
    --client-name MyClient

Author: Monkatraz

codegen-llm/.gitignore

@@ -0,0 +1,3 @@
+node_modules/
+dist/
+*.tsbuildinfo

codegen-llm/bin/codegen-llm.mjs

@@ -0,0 +1,2 @@
+#!/usr/bin/env node
+import("../dist/cli.js");