Add production documentation and feature flags (Phase 6)

Production preparation for Paykit integration:

- README.md: Comprehensive documentation including:
  - Architecture overview
  - Setup instructions (Gradle, jniLibs)
  - API usage examples
  - StateFlow observation pattern
  - Configuration options
  - Error handling guide
  - Production checklist
  - ProGuard rules
  - Rollback plan
  - Troubleshooting guide

- PaykitFeatureFlags.kt: Feature flag system including:
  - SharedPreferences-backed storage
  - Main enable/disable flag
  - Per-feature flags (Lightning, onchain, receipts)
  - Remote config integration (Firebase compatible)
  - Emergency rollback function

- PaykitConfigManager: Production configuration including:
  - Environment detection (dev/staging/prod)
  - Log level configuration
  - Timeout settings
  - Retry configuration
  - Error reporting callback

Author: JOHN

app/src/main/java/to/bitkit/paykit/PaykitFeatureFlags.kt

@@ -0,0 +1,172 @@
+package to.bitkit.paykit
+
+import android.content.Context
+import android.content.SharedPreferences
+import to.bitkit.utils.Logger
+
+/**
+ * Feature flags for Paykit integration.
+ *
+ * Use these flags to control the rollout of Paykit features
+ * and enable quick rollback if issues arise.
+ */
+object PaykitFeatureFlags {
+
+    private const val TAG = "PaykitFeatureFlags"
+    private const val PREFS_NAME = "paykit_feature_flags"
+
+    private const val ENABLED_KEY = "paykit_enabled"
+    private const val LIGHTNING_ENABLED_KEY = "paykit_lightning_enabled"
+    private const val ONCHAIN_ENABLED_KEY = "paykit_onchain_enabled"
+    private const val RECEIPT_STORAGE_ENABLED_KEY = "paykit_receipt_storage_enabled"
+
+    private var prefs: SharedPreferences? = null
+
+    /**
+     * Initialize feature flags with application context.
+     * Call this during Application.onCreate().
+     */
+    fun init(context: Context) {
+        prefs = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE)
+        setDefaults()
+    }
+
+    // MARK: - Main Feature Flag
+
+    /** Whether Paykit integration is enabled. */
+    var isEnabled: Boolean
+        get() = prefs?.getBoolean(ENABLED_KEY, false) ?: false
+        set(value) = prefs?.edit()?.putBoolean(ENABLED_KEY, value)?.apply() ?: Unit
+
+    /** Whether Lightning payments via Paykit are enabled. */
+    var isLightningEnabled: Boolean
+        get() = prefs?.getBoolean(LIGHTNING_ENABLED_KEY, true) ?: true
+        set(value) = prefs?.edit()?.putBoolean(LIGHTNING_ENABLED_KEY, value)?.apply() ?: Unit
+
+    /** Whether on-chain payments via Paykit are enabled. */
+    var isOnchainEnabled: Boolean
+        get() = prefs?.getBoolean(ONCHAIN_ENABLED_KEY, true) ?: true
+        set(value) = prefs?.edit()?.putBoolean(ONCHAIN_ENABLED_KEY, value)?.apply() ?: Unit
+
+    /** Whether receipt storage is enabled. */
+    var isReceiptStorageEnabled: Boolean
+        get() = prefs?.getBoolean(RECEIPT_STORAGE_ENABLED_KEY, true) ?: true
+        set(value) = prefs?.edit()?.putBoolean(RECEIPT_STORAGE_ENABLED_KEY, value)?.apply() ?: Unit
+
+    // MARK: - Remote Config
+
+    /**
+     * Update flags from remote config.
+     * Call this during app startup to sync with server-side configuration.
+     *
+     * @param config Map from remote config service (Firebase Remote Config, etc.)
+     */
+    fun updateFromRemoteConfig(config: Map<String, Any>) {
+        (config["paykit_enabled"] as? Boolean)?.let { isEnabled = it }
+        (config["paykit_lightning_enabled"] as? Boolean)?.let { isLightningEnabled = it }
+        (config["paykit_onchain_enabled"] as? Boolean)?.let { isOnchainEnabled = it }
+        (config["paykit_receipt_storage_enabled"] as? Boolean)?.let { isReceiptStorageEnabled = it }
+    }
+
+    // MARK: - Defaults
+
+    /** Set default values for all flags. */
+    private fun setDefaults() {
+        prefs?.let { p ->
+            if (!p.contains(ENABLED_KEY)) {
+                p.edit()
+                    .putBoolean(ENABLED_KEY, false) // Disabled by default until ready
+                    .putBoolean(LIGHTNING_ENABLED_KEY, true)
+                    .putBoolean(ONCHAIN_ENABLED_KEY, true)
+                    .putBoolean(RECEIPT_STORAGE_ENABLED_KEY, true)
+                    .apply()
+            }
+        }
+    }
+
+    // MARK: - Rollback
+
+    /**
+     * Emergency rollback - disable all Paykit features.
+     * Call this if critical issues are detected.
+     */
+    fun emergencyRollback() {
+        isEnabled = false
+        Logger.warn("Paykit emergency rollback triggered", context = TAG)
+
+        // Reset manager state
+        PaykitManager.getInstance().reset()
+    }
+}
+
+/**
+ * Manages Paykit configuration for production deployment.
+ */
+object PaykitConfigManager {
+
+    private const val TAG = "PaykitConfigManager"
+
+    // MARK: - Environment
+
+    /** Current environment configuration. */
+    val environment: PaykitEnvironment
+        get() = if (to.bitkit.BuildConfig.DEBUG) {
+            PaykitEnvironment.DEVELOPMENT
+        } else {
+            PaykitEnvironment.PRODUCTION
+        }
+
+    // MARK: - Logging
+
+    /** Log level for Paykit operations. */
+    var logLevel: PaykitLogLevel = PaykitLogLevel.INFO
+
+    /** Whether to log payment details (disable in production for privacy). */
+    val logPaymentDetails: Boolean
+        get() = to.bitkit.BuildConfig.DEBUG
+
+    // MARK: - Timeouts
+
+    /** Default payment timeout in milliseconds. */
+    var defaultPaymentTimeoutMs: Long = 60_000L
+
+    /** Lightning payment polling interval in milliseconds. */
+    var lightningPollingIntervalMs: Long = 500L
+
+    // MARK: - Retry Configuration
+
+    /** Maximum number of retry attempts for failed payments. */
+    var maxRetryAttempts: Int = 3
+
+    /** Base delay between retries in milliseconds. */
+    var retryBaseDelayMs: Long = 1000L
+
+    // MARK: - Monitoring
+
+    /**
+     * Error reporting callback.
+     * Set this to integrate with your error monitoring service.
+     */
+    var errorReporter: ((Throwable, Map<String, Any>?) -> Unit)? = null
+
+    /** Report an error to the configured monitoring service. */
+    fun reportError(error: Throwable, context: Map<String, Any>? = null) {
+        errorReporter?.invoke(error, context)
+    }
+}
+
+/** Paykit environment configuration. */
+enum class PaykitEnvironment {
+    DEVELOPMENT,
+    STAGING,
+    PRODUCTION
+}
+
+/** Log level for Paykit operations. */
+enum class PaykitLogLevel {
+    DEBUG,
+    INFO,
+    WARNING,
+    ERROR,
+    NONE
+}