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>

core/scraper.md

@@ -11,7 +11,7 @@ from core.scraper import handle_message, backfill_all, register_handlers, warm_e
 ### `handle_message(client, bot, msg, source_name, patterns, password=None)`
 **async.** Full pipeline for one document message:
 1. Extract filename + size, check allowlist + size guard
-2. Check `utils.cache` — skip if already seen
+2. Check `utils.cache` - skip if already seen
 3. Try `tdl` download → Telethon fallback
 4. `core.processor.process_file()` → hits
 5. `core.notifier.notify()` if hits found