Fix TestPythonApp CI failures on all three platforms

- macOS arm64: replace setup-ffmpeg action (x64-only) with brew install
- Cron scheduler tests: start db_write_queue in conftest so _execute_safe
  can process queued tasks; without it events never fired within timeout
- Stats dashboard test: reading_speed is now 79 (single-line sessions no
  longer contribute to active_time, changing the weighted average)

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

Author: bpwhelan

.github/workflows/test_python.yml

@@ -49,7 +49,12 @@ jobs:
       - name: Sync dependencies (project + dev)
         run: uv sync --extra dev
 
-      - name: Install ffmpeg
+      - name: Install ffmpeg (macOS)
+        if: runner.os == 'macOS'
+        run: brew install ffmpeg
+
+      - name: Install ffmpeg (non-macOS)
+        if: runner.os != 'macOS'
         uses: federicocarboni/setup-ffmpeg@v3
 
       # - name: Check Python formatting

tests/util/cron/conftest.py

@@ -0,0 +1,8 @@
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def _ensure_db_write_queue_running():
+    from GameSentenceMiner.util.database.write_queue import db_write_queue
+    db_write_queue.start()
+    yield

tests/web/test_stats_dashboard_e2e.py

@@ -436,7 +436,7 @@ def test_api_stats_full_flow_returns_expected_dashboard_contract(
     assert all_games["total_characters"] == 132
     assert all_games["total_sentences"] == 10
     assert all_games["total_time_hours"] == pytest.approx(1.675)
-    assert all_games["reading_speed"] == 78
+    assert all_games["reading_speed"] == 79
     assert all_games["sessions"] == 4
     assert all_games["completed_games"] == 1
     assert all_games["first_date"] == "2026-03-10"