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/providers/providers.go

@@ -0,0 +1,3 @@
+// Package providers handles loading and managing API key provider definitions.
+// Provider YAML files are loaded from the embedded filesystem (Plan 02).
+package providers

pkg/providers/registry_test.go

@@ -0,0 +1,23 @@
+package providers_test
+
+import (
+	"testing"
+)
+
+// TestRegistryLoad verifies that provider YAML files are loaded from embed.FS.
+// Stub: will be implemented when registry.go exists (Plan 02).
+func TestRegistryLoad(t *testing.T) {
+	t.Skip("stub — implement after registry.go exists")
+}
+
+// TestProviderSchemaValidation verifies format_version and last_verified are required.
+// Stub: will be implemented when schema.go validation exists (Plan 02).
+func TestProviderSchemaValidation(t *testing.T) {
+	t.Skip("stub — implement after schema.go validation exists")
+}
+
+// TestAhoCorasickBuild verifies Aho-Corasick automaton builds from provider keywords.
+// Stub: will be implemented when registry builds automaton (Plan 02).
+func TestAhoCorasickBuild(t *testing.T) {
+	t.Skip("stub — implement after registry AC build exists")
+}