chore(01-01): initialize Go module with Phase 1 dependencies

- go mod init github.com/salvacybersec/keyhunter
- Pin cobra v1.10.2, viper v1.21.0, ants v2.12.0 to exact versions
- Add modernc.org/sqlite v1.48.1 (CGO-free, pure Go)
- Add petar-dambovaliev/aho-corasick, x/crypto, x/time, lipgloss, testify
- tools.go with build tag to pin dependencies not yet imported in production code

tools.go

@@ -0,0 +1,19 @@
+//go:build tools
+
+// Package main contains tool imports to ensure Phase 1 dependencies are pinned in go.mod.
+// This file uses the standard Go tools pattern to track direct dependencies
+// that are not yet imported by production code but will be used in later plans.
+package main
+
+import (
+	_ "github.com/charmbracelet/lipgloss"
+	_ "github.com/panjf2000/ants/v2"
+	_ "github.com/petar-dambovaliev/aho-corasick"
+	_ "github.com/spf13/cobra"
+	_ "github.com/spf13/viper"
+	_ "github.com/stretchr/testify/assert"
+	_ "golang.org/x/crypto/argon2"
+	_ "golang.org/x/time/rate"
+	_ "gopkg.in/yaml.v3"
+	_ "modernc.org/sqlite"
+)