feat(whatsapp): add debounceMs for batching rapid messages (#971)

* feat(whatsapp): add debounceMs for batching rapid messages

Add a `debounceMs` configuration option to WhatsApp channel settings
that batches rapid consecutive messages from the same sender into a
single response. This prevents triggering separate agent runs for
each message when a user sends multiple short messages in quick
succession (e.g., "Hey!", "how are you?", "I was wondering...").

Changes:
- Add `debounceMs` config to WhatsAppConfig and WhatsAppAccountConfig
- Implement message buffering in `monitorWebInbox` with:
  - Map-based buffer keyed by sender (DM) or chat ID (groups)
  - Debounce timer that resets on each new message
  - Message combination with newline separator
  - Single message optimization (no modification if only one message)
- Wire `debounceMs` through account resolution and monitor tuning
- Add UI hints and schema documentation

Usage example:
{
  "channels": {
    "whatsapp": {
      "debounceMs": 5000  // 5 second window
    }
  }
}

Default behavior: `debounceMs: 0` (disabled by default)

Verified: All existing tests pass (3204 tests), TypeScript compilation
succeeds with no errors.

Implemented with assistance from AI coding tools.

Closes #967

* chore: wip inbound debounce

* fix: debounce inbound messages across channels (#971) (thanks @juanpablodlc)

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

docs/concepts/messages.md

@@ -33,6 +33,16 @@ Channels can redeliver the same message after reconnects. Clawdbot keeps a
 short-lived cache keyed by channel/account/peer/session/message id so duplicate
 deliveries do not trigger another agent run.
 
+## Inbound debouncing
+
+Rapid consecutive messages from the **same sender** can be batched into a single
+agent turn via `messages.inbound`. Debouncing is scoped per channel + conversation
+and uses the most recent message for reply threading/IDs.
+
+Notes:
+- Debounce applies to **text-only** messages; media/attachments flush immediately.
+- Control commands bypass debouncing so they remain standalone.
+
 ## Sessions and devices
 
 Sessions are owned by the gateway, not by clients.