Closes two silent-drift classes that hit three times in a single day
(2026-04-21) during the Arc 1 wave 2 cascade:

## Fix 1 — codegen-vscode auto-installs deps

Before: `just codegen-vscode` assumed `editors/vscode/node_modules`
was already populated. When it wasn't (fresh worktree, CI runner,
release PR checkout), the npx json2ts step failed with "could not
determine executable to run" — but `codegen-rust` + `codegen-dagster`
had already written their outputs, so half the pipeline had run. If
the dev didn't notice the error scroll and committed anyway, the
partial state landed on main and codegen-drift.yml fired on the next
PR. Happened to me on PR #204, and to whoever ran codegen for the
v1.12.0 release PR (#207 → #210 hotfix).

After: the recipe checks for node_modules and runs `npm install`
automatically. ~15s cost on a cold cache, skipped when deps are
present. Same self-heal pattern codegen-dagster already uses via
`uv run`.

## Fix 2 — new `codegen-all` recipe bundles regen-fixtures

Before: `just codegen` regenerated schemas + bindings but not
fixtures. Engine version bumps cascaded every fixture's `"version"`
field out of sync (hit on PR #207 release). The muscle memory was
"run codegen and you're done", which was wrong for anything
touching output shapes or version strings.

After: `just codegen-all` runs codegen + regen-fixtures together.
Kept `codegen` as the fast dev loop (~30s) and `codegen-all` as the
slower release loop (~1-2 min of extra fixture regen). Docstring on
`codegen` now points at `codegen-all` for the cases where it's the
right tool.

## Verification

- [x] Deleted `editors/vscode/node_modules`, ran `just codegen` — self-heal kicked in, npm install ran, codegen completed cleanly, `git status` shows only `justfile` modified (idempotent against main).
- [x] `just --list` shows both `codegen` and `codegen-all`.

## Not in scope (noted for follow-up if needed)

- Upfront preflight check (Fix B from the discussion) — decided against, because the self-heal in Fix 1 makes it redundant. Both dagster (uv-managed) and vscode (npm-managed) codegen steps now recover from missing deps on their own.
- Pre-commit hook additions — `.git-hooks/pre-commit` already runs codegen drift detection when schema files are staged; opt-in via `just install-hooks`. Making it default-on is a separate discussion about solo-project friction.