Rename to stealergram, add pyproject.toml, purge em-dashes

- Rename project to stealergram throughout
- Add pyproject.toml (replaces requirements.txt split, folds pytest.ini)
- Replace all em-dashes with hyphens across all source files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tui/events.py

@@ -1,5 +1,5 @@
 """
-tui_events.py — Thread-safe event bus between the bot backend and the TUI.
+tui_events.py - Thread-safe event bus between the bot backend and the TUI.
 
 The bot backend runs in a dedicated thread with its own asyncio event loop
 (completely isolated from Textual's loop).  Events are posted via a standard
@@ -18,7 +18,7 @@ import threading
 from dataclasses import dataclass, field
 from typing import Any
 
-# Thread-safe queue — works across the bot thread and Textual's thread.
+# Thread-safe queue - works across the bot thread and Textual's thread.
 _queue: queue.Queue | None = None
 _queue_lock = threading.Lock()