feat(01-02): embed loader, registry with Aho-Corasick, and filled test stubs

- loader.go with go:embed definitions/*.yaml for compile-time embedding
- registry.go with List(), Get(), Stats(), AC() methods
- Aho-Corasick automaton built from all provider keywords at NewRegistry()
- pkg/providers/definitions/ with 3 YAML files for embed
- All 5 provider tests pass: load, get, stats, AC, schema validation

pkg/providers/loader.go

@@ -0,0 +1,37 @@
+package providers
+
+import (
+	"embed"
+	"fmt"
+	"io/fs"
+	"path/filepath"
+
+	"gopkg.in/yaml.v3"
+)
+
+//go:embed definitions/*.yaml
+var definitionsFS embed.FS
+
+// loadProviders reads all YAML files from the embedded definitions FS.
+func loadProviders() ([]Provider, error) {
+	var providers []Provider
+	err := fs.WalkDir(definitionsFS, "definitions", func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() || filepath.Ext(path) != ".yaml" {
+			return nil
+		}
+		data, err := definitionsFS.ReadFile(path)
+		if err != nil {
+			return fmt.Errorf("reading provider file %s: %w", path, err)
+		}
+		var p Provider
+		if err := yaml.Unmarshal(data, &p); err != nil {
+			return fmt.Errorf("parsing provider %s: %w", path, err)
+		}
+		providers = append(providers, p)
+		return nil
+	})
+	return providers, err
+}