fix(dev): spawn turbo via shell so pnpm dev works on Windows

[scommisso]

What

Fixes pnpm dev on Windows, which currently crashes on startup:

[dev] web + client running on http://localhost:3838
Error: spawn turbo ENOENT
    syscall: 'spawn turbo', path: 'turbo', spawnargs: [ 'run', 'dev' ]

scripts/dev.mjs spawns turbo with a bare command name and an args array. On Windows the turbo binary is a turbo.cmd shim, which Node's spawn cannot exec by name without a shell, so it throws ENOENT and pnpm dev dies.

Why this fix

• shell: true so Windows resolves the .cmd shim (POSIX still works via /bin/sh).
• Pass the command as a single string ('turbo run dev') rather than an args array. Under shell: true an args array triggers Node's DEP0190 warning; the single-string form avoids it, and the arguments are static so there is no injection risk.

Also adds a note to .env.example: under turbo the web task runs with cwd=web/, so a relative ENGY_DIR resolves against web/ (e.g. web/.dev-engy/) rather than the repo root. Use an absolute path to point both web and client at one shared dev data store (otherwise the dev DB silently splits).

Validation

• pnpm dev now starts cleanly on Windows 11 (Node v24): turbo 2.8.12 spawns, no ENOENT, no DEP0190 warning, web + client come up and serve requests.
• node --check scripts/dev.mjs passes.
• Scope is limited to the dev launcher script and an env-template comment (no app/runtime code), so the full pnpm blt suite was not run.

Notes for reviewer

• Pre-existing (not introduced here): eslint scripts/dev.mjs reports no-undef for process/console because no Node globals are configured for the scripts/ dir. Out of scope; happy to add an eslint override in a follow-up.

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