Phase 7: Directory restructuring (messaging/ and tests/)

- Create messaging/platforms/ (base, discord, telegram, factory)
- Create messaging/rendering/ (discord_markdown, telegram_markdown)
- Create messaging/trees/ (data, repository, processor, queue_manager)
- Organize tests/ into api/, providers/, messaging/, cli/, config/
- Add backward-compatible re-exports at old locations
- Update handler.py and test_messaging_factory.py imports
- Fix Telegram type hints for TELEGRAM_AVAILABLE=False case
- Fix Python 3 except syntax in discord_markdown

Co-authored-by: Ali Khokhar <alishahryar2@gmail.com>

messaging/trees/__init__.py

@@ -0,0 +1,11 @@
+"""Message tree data structures and queue management."""
+
+from .data import MessageTree, MessageNode, MessageState
+from .queue_manager import TreeQueueManager
+
+__all__ = [
+    "TreeQueueManager",
+    "MessageTree",
+    "MessageNode",
+    "MessageState",
+]