feat: validate function code on deploy (catch syntax errors)

[MajorTal]

Problem

Deployed a function with a runtime error (used db.sql() with $1 params before that feature existed). Deploy succeeded — the error only surfaced when the function was invoked. No feedback until a user hit the broken code path.

Suggested Solution

Add basic validation during run402 functions deploy:

• node --check <file> catches syntax errors
• Optionally, a --validate flag that does a dry-run import

Even catching obvious syntax errors would save significant debugging time.

Context

Spent 3 deploy cycles debugging a function that could have been caught at deploy time.