#20594: feat(whatsapp): batch multi-image messages via debouncer

## Summary When multiple images are sent in rapid succession on WhatsApp (e.g., photo albums), this PR enables batching them into a single agent turn instead of processing each image separately. ## Problem Currently, sending 3 images results in 3 separate agent turns. This: - Increases API costs (3x tokens) - Loses context between images (agent responds to image 1 before seeing image 2) - Doesn't match user intent (they meant 'look at these 3 things together') ## Solution Leverage the existing `debounceMs` config and `MediaPaths` infrastructure (already used by iMessage, Discord, Telegram) for WhatsApp: 1. **Collect media paths** when batching debounced messages 2. **Pass `MediaPaths`/`MediaTypes`** arrays to the agent context 3. **Backwards compatible** - default `debounceMs` remains 0 (disabled) ## Usage Enable with config: ```yaml channels: whatsapp: debounceMs: 1500 # 1.5 second window for batching ``` ## Changes - `src/web/inbound/types.ts`: Add `mediaPaths`, `mediaTypes`, `mediaFileNames` to `WebInboundMessage` - `src/web/inbound/monitor.ts`: Collect all media in `onFlush` when batching - `src/web/auto-reply/monitor/process-message.ts`: Pass `MediaPaths`/`MediaTypes`/`MediaUrls` to context ## Testing - Build passes ✅ - Follows existing pattern from iMessage/Discord/Telegram implementations <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR enables WhatsApp to batch multiple images sent in rapid succession into a single agent turn, leveraging the existing `debounceMs` config and `MediaPaths` infrastructure already used by iMessage, Discord, and Telegram. **Key changes:** - Added `mediaPaths`, `mediaTypes`, and `mediaFileNames` arrays to `WebInboundMessage` type - Modified `onFlush` handler in `monitor.ts` to collect all media from batched messages - Updated `process-message.ts` to pass batched media arrays (`MediaPaths`, `MediaTypes`, `MediaUrls`) to agent context **Implementation details:** - Uses `> 0` check (fixed in commit 22ca7ef) to ensure single media items aren't lost, matching Discord/iMessage/Telegram pattern - Sets `MediaUrls` to `mediaPaths` for local file paths, consistent with other channels - Backwards compatible - default `debounceMs` remains 0 (disabled) The implementation correctly follows established patterns from other channels and addresses the issue raised in previous review comments. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The implementation follows established patterns from Discord, iMessage, and Telegram channels. The previously identified issue with `> 1` vs `> 0` comparison has been fixed in commit 22ca7ef. The changes are minimal, well-scoped, and backwards compatible (disabled by default). The code correctly batches media paths, types, and filenames when multiple messages are debounced. - No files require special attention _{Last reviewed commit: 22ca7ef} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->