Add structured logging with timestamps

[Lucasmind]

Priority: LOW

Problem

Logging is console-only with no timestamps or structured format. This makes debugging production issues difficult — you can't correlate events across services or measure performance.

Current Behavior

// utils/logger.js
log('TTS synthesize: "Hello world"');

Suggested Fix

Replace with structured JSON logging:

// utils/logger.js
const LOG_LEVELS = { debug: 0, info: 1, warn: 2, error: 3 };
let currentLevel = LOG_LEVELS.info;

export function setLogLevel(level) {
  currentLevel = LOG_LEVELS[level] ?? LOG_LEVELS.info;
}

export function log(level, event, data = {}) {
  if (LOG_LEVELS[level] < currentLevel) return;
  const entry = {
    timestamp: new Date().toISOString(),
    level,
    event,
    ...data
  };
  const method = level === 'error' ? 'error' : level === 'warn' ? 'warn' : 'log';
  console[method](JSON.stringify(entry));
}

Example Usage

log('info', 'tts.synthesize', { charCount: 11, voice: 'af_bella', queueLength: 2 });
log('error', 'llm.stream_failed', { status: 503, retryCount: 2 });
log('info', 'state.transition', { from: 'THINKING', to: 'SPEAKING' });

This enables:

• Performance measurement (add duration fields)
• Filtering by event type
• Correlating issues across pipeline stages

Files Affected

• frontend/src/utils/logger.js
• All files that import logger (update call sites)