chore(env): add sandbox integration env template

Signed-off-by: Vitor Mattos <vitor@php.rio>

Author: vitormattos

.env.example

@@ -0,0 +1,20 @@
+# Local sandbox setup for nfse-php smoke tests
+# Copy to .env.local and fill the secret values.
+
+# Full HEAD URL for sandbox mTLS smoke test
+# Example:
+# NFSE_HEAD_URL="https://adn.producaorestrita.nfse.gov.br/dps/00000000000000000000000000000000000000000000"
+NFSE_HEAD_URL="https://adn.producaorestrita.nfse.gov.br/dps/CHANGE_ME"
+
+# PFX certificate used for mTLS (local file, never commit)
+NFSE_MTLS_PFX_PATH=".secrets/pfx/2025-LibreCode.pfx"
+NFSE_MTLS_PFX_PASSWORD="CHANGE_ME"
+
+# Optional: set to 1 to print TLS handshake details
+NFSE_CURL_VERBOSE=0
+
+# Optional OpenBao/Vault settings (if needed by local app wiring)
+VAULT_ADDR="http://openbao:8200"
+VAULT_TOKEN=""
+VAULT_ROLE_ID=""
+VAULT_SECRET_ID=""