feat(tui): zebra striping, detail breadcrumb, sparkline stats, collapse persistence

Add alternating row backgrounds for easier table scanning. Detail panel
now shows breadcrumb path (Sites > Group > Name) and min/avg/max latency
stats below the sparkline. Group collapse state persists across restarts
via new preferences table in both SQLite and Postgres.

internal/store/postgres.go

@@ -67,6 +67,10 @@ func (d *PostgresDialect) CreateTablesSQL() []string {
 			created_by TEXT DEFAULT '',
 			created_at TIMESTAMP DEFAULT NOW()
 		)`,
+		`CREATE TABLE IF NOT EXISTS preferences (
+			key TEXT PRIMARY KEY,
+			value TEXT NOT NULL
+		)`,
 	}
 }
 

internal/store/sqlite.go

@@ -67,6 +67,10 @@ func (d *SQLiteDialect) CreateTablesSQL() []string {
 			created_by TEXT DEFAULT '',
 			created_at DATETIME DEFAULT CURRENT_TIMESTAMP
 		)`,
+		`CREATE TABLE IF NOT EXISTS preferences (
+			key TEXT PRIMARY KEY,
+			value TEXT NOT NULL
+		)`,
 	}
 }
 

internal/store/sqlstore.go

@@ -441,6 +441,24 @@ func (s *SQLStore) IsMonitorInMaintenance(monitorID int) (bool, error) {
 	return count > 0, nil
 }
 
+func (s *SQLStore) GetPreference(key string) (string, error) {
+	var value string
+	err := s.db.QueryRow(s.q("SELECT value FROM preferences WHERE key = ?"), key).Scan(&value)
+	if err != nil {
+		return "", err
+	}
+	return value, nil
+}
+
+func (s *SQLStore) SetPreference(key, value string) error {
+	if s.dollar {
+		_, err := s.db.Exec(s.q("INSERT INTO preferences (key, value) VALUES (?, ?) ON CONFLICT (key) DO UPDATE SET value = ?"), key, value, value)
+		return err
+	}
+	_, err := s.db.Exec("INSERT OR REPLACE INTO preferences (key, value) VALUES (?, ?)", key, value)
+	return err
+}
+
 func (s *SQLStore) ExportData() (models.Backup, error) {
 	sites, err := s.GetSites()
 	if err != nil {

internal/store/store.go

@@ -57,6 +57,10 @@ type Store interface {
 	DeleteMaintenanceWindow(id int) error
 	IsMonitorInMaintenance(monitorID int) (bool, error)
 
+	// Preferences
+	GetPreference(key string) (string, error)
+	SetPreference(key, value string) error
+
 	// Backup & Restore
 	ExportData() (models.Backup, error)
 	ImportData(data models.Backup) error