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>

web/dependencies.py

@@ -1,5 +1,5 @@
 """
-web/dependencies.py — FastAPI dependency functions.
+web/dependencies.py - FastAPI dependency functions.
 
 get_current_user: reads the access_token cookie, decodes + validates it,
                   loads the user row from web.db. Raises 401 if anything fails.