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/processor.md

@@ -54,8 +54,8 @@ Nested archives are recursed **one level** only.
 
 ## Password order
 
-1. `extra_password` (from message/channel carry-forward) — tried first
-2. `config.ARCHIVE_PASSWORDS` — tried in order
+1. `extra_password` (from message/channel carry-forward) - tried first
+2. `config.ARCHIVE_PASSWORDS` - tried in order
 
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