Stage 1: project skeleton, SQLite, migrations, HTTP server

- go mod init with chi, modernc.org/sqlite, golang.org/x/crypto
- Custom embedded migration runner (no CGO dependency)
- Config from TERDUT_ADDR / TERDUT_DB_PATH env vars
- chi router with /healthz endpoint
- Graceful shutdown on SIGINT/SIGTERM

internal/db/migrations/001_foundation.sql

@@ -0,0 +1,2 @@
+-- Stage 1 foundation. No tables yet; subsequent migrations add schema.
+SELECT 1;