feat(01-01): create main.go, test scaffolding, and testdata fixtures

- main.go entry point (7 lines) delegates to cmd.Execute()
- cmd/root.go stub so go build ./... compiles (Plan 05 replaces)
- pkg/providers, pkg/storage, pkg/engine package stubs
- Test stubs with t.Skip() for providers, storage, engine packages
- testdata/samples: openai_key.txt, anthropic_key.txt, multiple_keys.txt, no_keys.txt
- go build ./... and go test ./... -short both exit 0

pkg/storage/db_test.go

@@ -0,0 +1,23 @@
+package storage_test
+
+import (
+	"testing"
+)
+
+// TestDBOpen verifies SQLite database opens and creates schema.
+// Stub: will be implemented when db.go exists (Plan 03).
+func TestDBOpen(t *testing.T) {
+	t.Skip("stub — implement after db.go exists")
+}
+
+// TestEncryptDecryptRoundtrip verifies AES-256-GCM encrypt/decrypt roundtrip.
+// Stub: will be implemented when encrypt.go exists (Plan 03).
+func TestEncryptDecryptRoundtrip(t *testing.T) {
+	t.Skip("stub — implement after encrypt.go exists")
+}
+
+// TestArgon2KeyDerivation verifies Argon2id produces 32-byte key deterministically.
+// Stub: will be implemented when crypto.go exists (Plan 03).
+func TestArgon2KeyDerivation(t *testing.T) {
+	t.Skip("stub — implement after crypto.go exists")
+}