R2 event notifications

Do the Cloudflare setup first.

R2 puts a message on a queue for every object created under landing/. The writer pulls those messages, appends each named file, and deletes it, so it never lists the bucket. Files can arrive through the Worker from Files to R2, or straight through R2's S3 API from gateways that have their own R2 token. Use this mode instead of writer.py files, not alongside it.

npx wrangler queues create timelake-events
npx wrangler queues consumer http add timelake-events --batch-size 100 --message-retries 5 --visibility-timeout-secs 120
npx wrangler r2 bucket notification create timelake --event-type object-create --queue timelake-events --prefix landing/
npx wrangler queues info timelake-events      # note the queue ID
cat >> timelake.env <<'EOF'
export EVENTS_QUEUE_ID="<queue id>"
EOF

The writer's own writes go under lake/ and its deletes aren't object-create events, so they don't trigger notifications. The cron line:

* * * * * cd $HOME/timelake && . ./timelake.env && flock -n events.lock $HOME/.local/bin/uv run --with timelake --with boto3 writer.py events >> writer.log 2>&1

Try it with an upload through the Worker, as in Files to R2. A notification delivered twice finds the file already appended and deleted, and is skipped.