AGENTS.md has outdated notes on R2 rsync/rclone handling

[lautaropaske]

Commit 95307a3 replaced rsync (s3fs) with rclone.

AGENTS.md has a stale "R2 Storage Notes" section that still references s3fs/rsync/FUSE mounts, which were replaced by rclone in 95307a3; AGENTS.md udpate was missing.

proposed replacement for the "R2 Storage Notes" section:
R2 Storage
persistence uses rclone (S3 API, not FUSE). no s3fs, no rsync, no /data/moltbot.

• boot: rclone copy restores from R2 (additive). handles openclaw/ and legacy clawdbot/ prefixes.
• background sync: every 30s, rclone sync pushes changed files to R2 (with deletions). excludes *.lock, *.log, *.tmp, .git/**.
• manual sync: via sandbox.exec() in src/gateway/sync.ts.

sync delay is ~30s. data written between syncs is lost on container death.