feat(gateway): add BlueBubbles iMessage platform adapter (#6437)

Adds Apple iMessage as a gateway platform via BlueBubbles macOS server.

Architecture:
- Webhook-based inbound (event-driven, no polling/dedup needed)
- Email/phone → chat GUID resolution for user-friendly addressing
- Private API safety (checks helper_connected before tapback/typing)
- Inbound attachment downloading (images, audio, documents cached locally)
- Markdown stripping for clean iMessage delivery
- Smart progress suppression for platforms without message editing

Based on PR #5869 by @benjaminsehl (webhook architecture, GUID resolution,
Private API safety, progress suppression) with inbound attachment downloading
from PR #4588 by @1960697431 (attachment cache routing).

Integration points: Platform enum, env config, adapter factory, auth maps,
cron delivery, send_message routing, channel directory, platform hints,
toolset definition, setup wizard, status display.

27 tests covering config, adapter, webhook parsing, GUID resolution,
attachment download routing, toolset consistency, and prompt hints.

tools/send_message_tool.py

@@ -148,6 +148,7 @@ def _handle_send(args):
         "slack": Platform.SLACK,
         "whatsapp": Platform.WHATSAPP,
         "signal": Platform.SIGNAL,
+        "bluebubbles": Platform.BLUEBUBBLES,
         "matrix": Platform.MATRIX,
         "mattermost": Platform.MATTERMOST,
         "homeassistant": Platform.HOMEASSISTANT,
@@ -396,6 +397,8 @@ async def _send_to_platform(platform, pconfig, chat_id, message, thread_id=None,
             result = await _send_feishu(pconfig, chat_id, chunk, thread_id=thread_id)
         elif platform == Platform.WECOM:
             result = await _send_wecom(pconfig.extra, chat_id, chunk)
+        elif platform == Platform.BLUEBUBBLES:
+            result = await _send_bluebubbles(pconfig.extra, chat_id, chunk)
         else:
             result = {"error": f"Direct sending not yet implemented for {platform.value}"}
 
@@ -870,6 +873,33 @@ async def _send_wecom(extra, chat_id, message):
         return _error(f"WeCom send failed: {e}")
 
 
+async def _send_bluebubbles(extra, chat_id, message):
+    """Send via BlueBubbles iMessage server using the adapter's REST API."""
+    try:
+        from gateway.platforms.bluebubbles import BlueBubblesAdapter, check_bluebubbles_requirements
+        if not check_bluebubbles_requirements():
+            return {"error": "BlueBubbles requirements not met (need aiohttp + httpx)."}
+    except ImportError:
+        return {"error": "BlueBubbles adapter not available."}
+
+    try:
+        from gateway.config import PlatformConfig
+        pconfig = PlatformConfig(extra=extra)
+        adapter = BlueBubblesAdapter(pconfig)
+        connected = await adapter.connect()
+        if not connected:
+            return _error("BlueBubbles: failed to connect to server")
+        try:
+            result = await adapter.send(chat_id, message)
+            if not result.success:
+                return _error(f"BlueBubbles send failed: {result.error}")
+            return {"success": True, "platform": "bluebubbles", "chat_id": chat_id, "message_id": result.message_id}
+        finally:
+            await adapter.disconnect()
+    except Exception as e:
+        return _error(f"BlueBubbles send failed: {e}")
+
+
 async def _send_feishu(pconfig, chat_id, message, media_files=None, thread_id=None):
     """Send via Feishu/Lark using the adapter's send pipeline."""
     try: