Add SDK usage tracking to JSONL logs

Features:
- New UsageLogger utility that writes usage metrics to daily JSONL files
- Captures token counts, costs, timing, and cache metrics from SDK result messages
- Usage logs stored in ~/.claude-mem/usage-logs/ (one file per day)
- Added analyze-usage.js script for analyzing usage patterns

Usage data captured:
- Token counts (input, output, cache creation, cache read)
- Total cost in USD per API call
- Duration metrics (total and API time)
- Number of turns per session
- Session and project attribution

Analysis script features:
- Aggregates totals by project and model
- Shows cache hit rates and savings
- Displays cost breakdowns and averages
- npm scripts: usage:analyze and usage:today

Files:
- src/utils/usage-logger.ts (new)
- src/services/worker-service.ts (modified - captures SDK result messages)
- scripts/analyze-usage.js (new)
- package.json (added usage:* npm scripts)

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

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

package.json

@@ -38,7 +38,9 @@
     "worker:start": "pm2 start ecosystem.config.cjs",
     "worker:stop": "pm2 stop claude-mem-worker",
     "worker:restart": "pm2 restart claude-mem-worker",
-    "worker:logs": "pm2 logs claude-mem-worker"
+    "worker:logs": "pm2 logs claude-mem-worker",
+    "usage:analyze": "node scripts/analyze-usage.js",
+    "usage:today": "node scripts/analyze-usage.js $(date +%Y-%m-%d)"
   },
   "dependencies": {
     "@anthropic-ai/claude-agent-sdk": "^0.1.27",