Add automatic log rotation for daemon (bd-154)

- Integrated lumberjack library for production-ready log rotation
- Configurable via env vars: BEADS_DAEMON_LOG_MAX_SIZE, BEADS_DAEMON_LOG_MAX_BACKUPS, BEADS_DAEMON_LOG_MAX_AGE, BEADS_DAEMON_LOG_COMPRESS
- Defaults: 10MB max size, 3 backups, 7 day retention, compression enabled
- Added comprehensive tests for env var parsing and rotation config
- Updated README.md and CHANGELOG.md with rotation documentation
- Prevents unbounded log growth for long-running daemons

Amp-Thread-ID: https://ampcode.com/threads/T-8232d41a-6872-4f4c-962c-7fae8f5e83b7
Co-authored-by: Amp <amp@ampcode.com>

README.md

@@ -915,7 +915,7 @@ The daemon will:
 - Auto-push commits (if `--auto-push` flag set)
 - Pull remote changes periodically
 - Auto-import when remote changes detected
-- Log all activity to `.beads/daemon.log`
+- Log all activity to `.beads/daemon.log` with automatic rotation
 
 Options:
 ```bash
@@ -929,6 +929,14 @@ bd daemon --global                    # Run as global daemon (see below)
 bd daemon --migrate-to-global         # Migrate from local to global daemon
 ```
 
+Log rotation is automatic and configurable via environment variables:
+```bash
+export BEADS_DAEMON_LOG_MAX_SIZE=10      # Max log size in MB (default: 10)
+export BEADS_DAEMON_LOG_MAX_BACKUPS=3    # Number of rotated logs to keep (default: 3)
+export BEADS_DAEMON_LOG_MAX_AGE=7        # Max age of logs in days (default: 7)
+export BEADS_DAEMON_LOG_COMPRESS=true    # Compress rotated logs (default: true)
+```
+
 The daemon is ideal for:
 - Always-on development machines
 - Multi-agent workflows where agents need continuous sync