Make cargo ci regen exhaustive across committed codegen

This issue tracks reimplementing the work from stale PR #4300, which has been closed because it is too far out of date to merge directly.

Original pull request

• PR #4300: Make cargo ci regen exhaustive across all committed codegen
• Original author: @cloutiertyler

What the original PR was trying to do

Summary - Restructures cargo ci regen into 5 logical categories covering all committed codegen in the repo: 1. SDK test bindings — Rust (5 pairs), Cregression tests (3 pairs), Unreal (2 pairs) 2. Demo project bindings — Blackholio Unity C+ Unreal C++ 3. Starter template bindings — C, Rust, TS (auto-discovered via pnpm), deno-ts, Unreal QuickstartChat 4. SDK internal codegen — TS client-api, CClientApi, TS test-app, TS test-react-router-app 5. Moduledef type bindings — C, TS, C++, Unreal SDK - Adds generate scripts to 5 TS templates that were missing them (browser-ts, bun-ts, nodejs-ts, tanstack-ts, keynote-2) - Adds 5 missing templates to pnpm-workspace.yaml (bun-ts, nodejs-ts, nextjs-ts, remix-ts, keynote-2) - Adds autogen coverage check (--check mode) that scans the repo for autogen markers and errors if any directory isn't in the REGEN_DIRS allowlist - A...

Closure context

• Way stale. Going to close this and create a ticket to track its implementation. This PR is a good starting point though. Assign it to me.

Reimplementation notes

• Reimplement this work on top of current master in a new PR.
• Keep the original PR linked as historical context and as a source of useful implementation ideas where still relevant.