feat: add comprehensive logging system with file output

- Add backend logging to logs/backend.log with file rotation support
- Add frontend logging to logs/frontend.log via /api/logs endpoint
- Add frontend logger utility with batching and user context
- Update .gitignore to exclude log files but preserve logs directory
- Update CLAUDE.md with logging documentation and usage examples

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/backend/config.js

@@ -1,12 +1,18 @@
 import Database from 'bun:sqlite';
 import { drizzle } from 'drizzle-orm/bun-sqlite';
 import * as schema from './db/schema/index.js';
-import { join } from 'path';
+import { join, dirname } from 'path';
+import { existsSync, mkdirSync } from 'fs';
+import { fileURLToPath } from 'url';
 
 // ===================================================================
 // Configuration
 // ===================================================================
 
+// ES module equivalent of __dirname
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
 const isDevelopment = process.env.NODE_ENV !== 'production';
 
 export const JWT_SECRET = process.env.JWT_SECRET || 'your-secret-key-change-in-production';
@@ -19,16 +25,46 @@ export const LOG_LEVEL = process.env.LOG_LEVEL || (isDevelopment ? 'debug' : 'in
 const logLevels = { debug: 0, info: 1, warn: 2, error: 3 };
 const currentLogLevel = logLevels[LOG_LEVEL] ?? 1;
 
+// Log file paths
+const logsDir = join(__dirname, '../../logs');
+const backendLogFile = join(logsDir, 'backend.log');
+
+// Ensure log directory exists
+if (!existsSync(logsDir)) {
+  mkdirSync(logsDir, { recursive: true });
+}
+
+function formatLogMessage(level, message, data) {
+  const timestamp = new Date().toISOString();
+  let logMessage = `[${timestamp}] ${level.toUpperCase()}: ${message}`;
+
+  if (data && Object.keys(data).length > 0) {
+    logMessage += ' ' + JSON.stringify(data, null, 2);
+  }
+
+  return logMessage + '\n';
+}
+
 function log(level, message, data) {
   if (logLevels[level] < currentLogLevel) return;
 
-  const timestamp = new Date().toISOString();
-  const logMessage = `[${timestamp}] ${level.toUpperCase()}: ${message}`;
+  const logMessage = formatLogMessage(level, message, data);
 
-  if (data && Object.keys(data).length > 0) {
-    console.log(logMessage, JSON.stringify(data, null, 2));
-  } else {
-    console.log(logMessage);
+  // Write to file asynchronously (fire and forget for performance)
+  Bun.write(backendLogFile, logMessage, { createPath: true }).catch(err => {
+    console.error('Failed to write to log file:', err);
+  });
+
+  // Also log to console in development
+  if (isDevelopment) {
+    const timestamp = new Date().toISOString();
+    const consoleMessage = `[${timestamp}] ${level.toUpperCase()}: ${message}`;
+
+    if (data && Object.keys(data).length > 0) {
+      console.log(consoleMessage, data);
+    } else {
+      console.log(consoleMessage);
+    }
   }
 }
 
@@ -39,6 +75,27 @@ export const logger = {
   error: (message, data) => log('error', message, data),
 };
 
+// Frontend logger - writes to separate log file
+const frontendLogFile = join(logsDir, 'frontend.log');
+
+export function logToFrontend(level, message, data = null, context = {}) {
+  if (logLevels[level] < currentLogLevel) return;
+
+  const timestamp = new Date().toISOString();
+  let logMessage = `[${timestamp}] [${context.userAgent || 'unknown'}] [${context.userId || 'anonymous'}] ${level.toUpperCase()}: ${message}`;
+
+  if (data && Object.keys(data).length > 0) {
+    logMessage += ' ' + JSON.stringify(data, null, 2);
+  }
+
+  logMessage += '\n';
+
+  // Write to frontend log file
+  Bun.write(frontendLogFile, logMessage, { createPath: true }).catch(err => {
+    console.error('Failed to write to frontend log file:', err);
+  });
+}
+
 export default logger;
 
 // ===================================================================
@@ -46,7 +103,6 @@ export default logger;
 // ===================================================================
 
 // Get the directory containing this config file, then go to parent for db location
-const __dirname = new URL('.', import.meta.url).pathname;
 const dbPath = join(__dirname, 'award.db');
 
 const sqlite = new Database(dbPath);