Add logging service

New Go program (logger/) that:
- Accepts POSTed JSON log messages via POST /log
- Stores last N messages in a ring buffer (default 1M)
- Retrieves logs via GET /logs with limit/before/after filters
- Shows status via GET /status

Also updates express/logging.ts to POST messages to the logger service.

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

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

logger/go.mod

@@ -0,0 +1,3 @@
+module philologue.net/diachron/logger-bin
+
+go 1.23.3