[IMP][P0] Add live API tools to invoice_review template

[mishrapravin114]

Type

Implementation — merge a PR with working code. Not investigation.

Goal

Wire invoice_review to fetch invoice data from HTTP API or file path (env-gated), with mock fallback.

Files to create or change

examples/templates/invoice_review/tools.py ← NEW
examples/templates/invoice_review/.env.example ← NEW
examples/templates/invoice_review/README.md ← UPDATE
examples/templates/invoice_review/nodes/__init__.py ← UPDATE if needed

Implementation checklist

• fetch_invoice(invoice_id: str) — mock JSON when INVOICE_USE_LIVE unset; else HTTP GET or read from INVOICE_FILE_DROP_DIR/{id}.json
• submit_approval_result(invoice_id, status, notes) — dry-run log unless INVOICE_API_WRITE=1
• ./engine validate examples/templates/invoice_review passes
• ./engine run examples/templates/invoice_review --input '{"invoice_id":"INV-001"}' works with mocks

Done when

• PR merged to main
• README documents AP exception flow + env vars
• No secrets in git

Out of scope

• Client-specific ERP connectors (SAP, NetSuite)
• Engine Cloud

Related (context only)

#15 integration playbook