Move documentation to docs/ directory and improve terminology

- Move ARCHITECTURE.md and CLAUDE.md to docs/ directory
- Replace "real-time" terminology with accurate "low-latency" and "high-performance"
- Update README to reflect correct performance characteristics
- Add comprehensive ICAO country database with SQLite backend
- Fix display options positioning and functionality
- Add map scale controls and improved range ring visibility
- Enhance aircraft marker orientation and trail management

🤖 Generated with [Claude Code](https://claude.ai/code)

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

internal/merger/merger.go

@@ -26,6 +26,7 @@ import (
 	"sync"
 	"time"
 
+	"skyview/internal/icao"
 	"skyview/internal/modes"
 )
 
@@ -72,6 +73,9 @@ type AircraftState struct {
 	MLATSources     []string               `json:"mlat_sources"`     // Sources providing MLAT position data
 	PositionSource  string                 `json:"position_source"`  // Source providing current position
 	UpdateRate      float64                `json:"update_rate"`      // Recent updates per second
+	Country         string                 `json:"country"`          // Country of registration
+	CountryCode     string                 `json:"country_code"`     // ISO country code
+	Flag            string                 `json:"flag"`             // Country flag emoji
 }
 
 // MarshalJSON provides custom JSON marshaling for AircraftState to format ICAO24 as hex.
@@ -221,6 +225,7 @@ type SpeedPoint struct {
 type Merger struct {
 	aircraft      map[uint32]*AircraftState // ICAO24 -> merged aircraft state
 	sources       map[string]*Source        // Source ID -> source information
+	icaoDB        *icao.Database            // ICAO country lookup database
 	mu            sync.RWMutex              // Protects all maps and slices
 	historyLimit  int                      // Maximum history points to retain
 	staleTimeout  time.Duration             // Time before aircraft considered stale (15 seconds)
@@ -242,14 +247,20 @@ type updateMetric struct {
 //   - Update metrics tracking enabled
 //
 // The merger is ready for immediate use after creation.
-func NewMerger() *Merger {
+func NewMerger() (*Merger, error) {
+	icaoDB, err := icao.NewDatabase()
+	if err != nil {
+		return nil, fmt.Errorf("failed to initialize ICAO database: %w", err)
+	}
+
 	return &Merger{
 		aircraft:      make(map[uint32]*AircraftState),
 		sources:       make(map[string]*Source),
+		icaoDB:        icaoDB,
 		historyLimit:  500,
 		staleTimeout:  15 * time.Second, // Aircraft timeout - reasonable for ADS-B tracking
 		updateMetrics: make(map[uint32]*updateMetric),
-	}
+	}, nil
 }
 
 // AddSource registers a new data source with the merger.
@@ -304,6 +315,19 @@ func (m *Merger) UpdateAircraft(sourceID string, aircraft *modes.Aircraft, signa
 			AltitudeHistory: make([]AltitudePoint, 0),
 			SpeedHistory:    make([]SpeedPoint, 0),
 		}
+		
+		// Lookup country information for new aircraft
+		if countryInfo, err := m.icaoDB.LookupCountry(fmt.Sprintf("%06X", aircraft.ICAO24)); err == nil {
+			state.Country = countryInfo.Country
+			state.CountryCode = countryInfo.CountryCode
+			state.Flag = countryInfo.Flag
+		} else {
+			// Fallback to unknown if lookup fails
+			state.Country = "Unknown"
+			state.CountryCode = "XX"
+			state.Flag = "🏳️"
+		}
+		
 		m.aircraft[aircraft.ICAO24] = state
 		m.updateMetrics[aircraft.ICAO24] = &updateMetric{
 			updates: make([]time.Time, 0),
@@ -777,3 +801,14 @@ func calculateDistanceBearing(lat1, lon1, lat2, lon2 float64) (float64, float64)
 
 	return distance, bearing
 }
+
+// Close closes the merger and releases resources
+func (m *Merger) Close() error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	
+	if m.icaoDB != nil {
+		return m.icaoDB.Close()
+	}
+	return nil
+}