Initial commit: project setup and db package

- Project scaffolding: go.mod, Makefile, .golangci.yaml, doc.go
- README, ARCHITECTURE, PROJECT_PLAN, PROGRESS documentation
- db package: Open (WAL, FK, busy timeout, 0600 permissions),
  Migrate (sequential, transactional, idempotent),
  SchemaVersion, Snapshot (VACUUM INTO)
- 11 tests covering open, migrate, and snapshot

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

doc.go

@@ -0,0 +1,7 @@
+// Package mcdsl is the Metacircular Dynamics Standard Library.
+//
+// It provides shared infrastructure packages for Metacircular services:
+// authentication, database setup, configuration loading, HTTP/gRPC server
+// bootstrapping, CSRF protection, session management, health checks, and
+// service directory snapshots.
+package mcdsl