feat: implement structured logging system throughout the codebase

- Add logger utility adapted from payload-mailing pattern
- Use PAYLOAD_BILLING_LOG_LEVEL environment variable for configuration
- Replace console.* calls with contextual loggers across providers
- Update webhook utilities to support proper logging
- Export logging utilities for external use
- Maintain fallback console logging for compatibility

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

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

src/utils/logger.ts

@@ -0,0 +1,48 @@
+import type { Payload } from 'payload'
+
+let pluginLogger: any = null
+
+/**
+ * Get or create the plugin logger instance
+ * Uses PAYLOAD_BILLING_LOG_LEVEL environment variable to configure log level
+ * Defaults to 'info' if not set
+ */
+export function getPluginLogger(payload: Payload) {
+  if (!pluginLogger && payload.logger) {
+    const logLevel = process.env.PAYLOAD_BILLING_LOG_LEVEL || 'info'
+
+    pluginLogger = payload.logger.child({
+      level: logLevel,
+      plugin: '@xtr-dev/payload-billing'
+    })
+
+    // Log the configured log level on first initialization
+    pluginLogger.info(`Logger initialized with level: ${logLevel}`)
+  }
+
+  // Fallback to console if logger not available (shouldn't happen in normal operation)
+  if (!pluginLogger) {
+    return {
+      debug: (...args: any[]) => console.log('[BILLING DEBUG]', ...args),
+      info: (...args: any[]) => console.log('[BILLING INFO]', ...args),
+      warn: (...args: any[]) => console.warn('[BILLING WARN]', ...args),
+      error: (...args: any[]) => console.error('[BILLING ERROR]', ...args),
+    }
+  }
+
+  return pluginLogger
+}
+
+/**
+ * Create a context-specific logger for a particular operation
+ */
+export function createContextLogger(payload: Payload, context: string) {
+  const logger = getPluginLogger(payload)
+
+  return {
+    debug: (message: string, ...args: any[]) => logger.debug(`[${context}] ${message}`, ...args),
+    info: (message: string, ...args: any[]) => logger.info(`[${context}] ${message}`, ...args),
+    warn: (message: string, ...args: any[]) => logger.warn(`[${context}] ${message}`, ...args),
+    error: (message: string, ...args: any[]) => logger.error(`[${context}] ${message}`, ...args),
+  }
+}