Resolve 21 pre-existing @typescript-eslint/no-unused-vars errors across
5 files (actions.ts, alert.ts, digest.ts, env.ts, worker/email.ts) that
were blocking the script/checks gate. All removals are unused imports
and unused variable assignments with no runtime impact.
Replace all Postmark references (POSTMARK_API_KEY, POSTMARK_SENDER_ADDRESS)
with SMTP configuration (SMTP_HOST, SMTP_PORT, SMTP_USER, SMTP_PASSWORD,
SMTP_FROM) across documentation, deployment config, template, and test.
- README.md: architecture diagram (Postmark → SMTP) and configuration table
- docker-compose.yml: POSTMARK_* env vars replaced with SMTP_* required vars
- .env.template: POSTMARK_* entries replaced with SMTP_* entries
- test/integration.sh: POSTMARK_* test exports replaced with SMTP_* test values
