fix(chatwoot-adapter): bound seen-marker growth with a 3-day TTL prune (#620)

[rmyndharis]

Summary

The Chatwoot adapter records one ctx.storage marker per relayed message, used to de-duplicate WhatsApp re-deliveries and to suppress the operator's own echoed sends. These markers were written once and never removed, so on a long-running instance the plugin's storage grew without bound, and the inbound-retry drain's periodic directory scan (storage.list, a full readdirSync plus a per-file key decode) grew steadily more expensive as the marker count climbed.

This change bounds the seen: keyspace with a time-based retention window.

Closes #620.

Changes

• Timestamped markers. markSeen now stores { t: <ms> } instead of a bare 1; hasSeen is unchanged (it still checks presence only). This gives every marker an age.
• pruneSeen(now, ttl). A new MappingStore primitive that streams the seen: keys and deletes any older than the retention window. A pre-existing marker (stored as a bare 1, with no timestamp) is adopted — re-stamped with the current time — rather than deleted, so the migration can never re-post a message as a duplicate; those adopted markers then age out one window later.
• Hourly prune. Wired onto the existing 30-second inbound-retry timer (no second timer), guarded by its own in-flight flag and kept independent of the retry drain so a prune never blocks a retry. It runs regardless of Chatwoot config validity, since it neither reads config nor relays.
• Retention window SEEN_TTL_MS is 3 days and the prune cadence is hourly — hardcoded constants, matching the existing retry-timer tuning.

Impact

• Fixes unbounded plugin-storage growth and keeps the retry drain's directory scan cheap on long-running instances.
• No configuration or operator action is required; existing markers migrate automatically on the first prune.
• The 3-day window comfortably outlasts any realistic WhatsApp re-delivery or own-send echo, so normal live de-duplication is unaffected.
• Adapter-only: no core, permission, or minOpenWAVersion change. Version 0.5.1 → 0.5.2 (patch).

Testing

• New mapping-store unit tests cover pruneSeen: TTL expiry, keeping recent markers, legacy-marker adoption (stamps rather than deletes), and touching only seen:-prefixed keys.
• Full plugin test suite: 272/272 passing. tsc --noEmit clean, catalog in sync, and chatwoot-adapter packages cleanly.