feat: add GeoIP country lookup with embedded DB-IP Lite database (PLAN.md 4.3)

Embeds a DB-IP Lite country MMDB (~5MB) in the binary via go:embed,
keeping the single-binary deployment story clean. Country codes are
stored alongside login attempts and sessions, shown in the dashboard
(Top IPs, Top Countries card, Recent/Active Sessions, session detail).

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

internal/storage/store.go

@@ -11,6 +11,7 @@ type LoginAttempt struct {
 	Username  string
 	Password  string
 	IP        string
+	Country   string
 	Count     int
 	FirstSeen time.Time
 	LastSeen  time.Time
@@ -20,6 +21,7 @@ type LoginAttempt struct {
 type Session struct {
 	ID             string
 	IP             string
+	Country        string
 	Username       string
 	ShellName      string
 	ConnectedAt    time.Time
@@ -54,18 +56,19 @@ type DashboardStats struct {
 
 // TopEntry represents a value and its count for top-N queries.
 type TopEntry struct {
-	Value string
-	Count int64
+	Value   string
+	Country string // populated by GetTopIPs
+	Count   int64
 }
 
 // Store is the interface for persistent storage of honeypot data.
 type Store interface {
 	// RecordLoginAttempt upserts a login attempt, incrementing the count
 	// for existing (username, password, ip) combinations.
-	RecordLoginAttempt(ctx context.Context, username, password, ip string) error
+	RecordLoginAttempt(ctx context.Context, username, password, ip, country string) error
 
 	// CreateSession creates a new session record and returns its UUID.
-	CreateSession(ctx context.Context, ip, username, shellName string) (string, error)
+	CreateSession(ctx context.Context, ip, username, shellName, country string) (string, error)
 
 	// EndSession sets the disconnected_at timestamp for a session.
 	EndSession(ctx context.Context, sessionID string, disconnectedAt time.Time) error
@@ -92,6 +95,9 @@ type Store interface {
 	// GetTopIPs returns the top N IPs by total attempt count.
 	GetTopIPs(ctx context.Context, limit int) ([]TopEntry, error)
 
+	// GetTopCountries returns the top N countries by total attempt count.
+	GetTopCountries(ctx context.Context, limit int) ([]TopEntry, error)
+
 	// GetRecentSessions returns the most recent sessions ordered by connected_at DESC.
 	// If activeOnly is true, only sessions with no disconnected_at are returned.
 	GetRecentSessions(ctx context.Context, limit int, activeOnly bool) ([]Session, error)