fix: _run_bench crashes when Engines tab was never opened (v2.1.2)

_stt_commit() accesses self.stt_name which only exists after the Engines
tab is lazily built. Guard with hasattr so running a benchmark directly
from the Benchmark tab no longer throws AttributeError.

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

linux/blitztext/__init__.py

@@ -6,4 +6,4 @@ counterpart to the macOS Blitztext menu bar app: it runs natively on the host
 (not in a container) so it can type into any application via xdotool.
 """
 
-__version__ = "2.1.1"
+__version__ = "2.1.2"

linux/blitztext/gtksettings.py

@@ -2073,7 +2073,8 @@ notebook.bt-nb tab:checked label {
             return
         reference = Path(refp).read_text(errors="replace")
         self.bench_store.clear()
-        self._stt_commit()
+        if hasattr(self, "stt_name"):   # only if Engines tab has been built
+            self._stt_commit()
 
         # Filter to checked engines (deduplicate by name as safety net)
         checks = getattr(self, "_bench_checks", {})