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/tdl_downloader.md

@@ -22,7 +22,7 @@ Used by the live handler and `bot_downloader`.
 
 ### `download_batch_with_tdl(entries: list[BatchEntry]) -> dict[int, bool]`
 **async.** Downloads up to `TDL_AMOUNT` messages in a single `tdl dl` invocation.  
-Returns `{doc_id: True|False}` — `False` means Telethon fallback needed.
+Returns `{doc_id: True|False}` - `False` means Telethon fallback needed.
 
 ---
 
@@ -55,7 +55,7 @@ In CLI mode: subprocess inherits the terminal, progress bars render natively.
 Each batch/single download gets a unique `data/tmp/_tdl_{monotonic_ns}/` staging dir.  
 After `tdl` exits, files are matched by name (with fuzzy stem fallback for `filenamify()` mangling) and moved to final `dest`. Staging dir is removed regardless of outcome.
 
-`--template '{{ filenamify .FileName }}'` — tdl uses the original Telegram filename, not its default `DialogID_MessageID_filename` format.
+`--template '{{ filenamify .FileName }}'` - tdl uses the original Telegram filename, not its default `DialogID_MessageID_filename` format.
 
 ---