feat: initialize Go module and project skeleton

- Initialize naviwatcher Go module
- Create directory structure: internal/config/, internal/database/, cmd/naviwatcher/
- Add main.go entry point with flag parsing, config loading placeholder, and graceful shutdown skeleton
- Add dependencies: go-sqlite3, yaml.v3
- Write tests for config loading and flag parsing
- All tests pass, go vet clean

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/naviwatcher/main_test.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadConfig_Defaults(t *testing.T) {
+	// The skeleton loadConfig applies defaults when host/port are zero-value.
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	if err := os.WriteFile(path, []byte("server:\n  host: \"\"\n  port: 0\n"), 0644); err != nil {
+		t.Fatalf("failed to write config: %v", err)
+	}
+
+	cfg, err := loadConfig(path)
+	if err != nil {
+		t.Fatalf("loadConfig returned error: %v", err)
+	}
+
+	if cfg.Server.Host != "0.0.0.0" {
+		t.Errorf("expected default host 0.0.0.0, got %q", cfg.Server.Host)
+	}
+	if cfg.Server.Port != 8080 {
+		t.Errorf("expected default port 8080, got %d", cfg.Server.Port)
+	}
+}
+
+func TestLoadConfig_FileNotFound(t *testing.T) {
+	_, err := loadConfig("/nonexistent/path/config.yaml")
+	if err == nil {
+		t.Fatal("expected error for missing file, got nil")
+	}
+}
+
+func TestParseYAML_Empty(t *testing.T) {
+	var cfg placeholderConfig
+	err := parseYAML([]byte(""), &cfg)
+	if err != nil {
+		t.Fatalf("parseYAML returned error for empty input: %v", err)
+	}
+}