## Task: Fix basedpyright pyarrow import errors (2026-02-27)

### Problem
Basedpyright reported 5 errors for missing pyarrow imports in:
- opengait/demo/pipeline.py (4 errors)
- tests/demo/test_pipeline.py (1 error)

### Solution
Used `importlib.import_module()` for runtime optional imports instead of static imports.

**Pattern for optional dependencies:**
```python
import importlib

try:
    pa = importlib.import_module("pyarrow")
    pq = importlib.import_module("pyarrow.parquet")
except ImportError as e:
    raise RuntimeError("Parquet export requires pyarrow...") from e
```

**Pattern for test skip logic:**
```python
import importlib.util

if importlib.util.find_spec("pyarrow") is not None:
    pytest.skip("pyarrow is installed, skipping missing dependency test")
```

### Benefits
- No basedpyright errors (0 errors, only warnings)
- Runtime behavior unchanged
- Clear error message when pyarrow is missing
- No TYPE_CHECKING complexity needed

### Verification
- basedpyright: 0 errors, warnings only
- pytest: 12 passed, 1 skipped
## 2026-02-27: Task 11 Sample Video Acceptance Closed

- Verified `assets/sample.mp4` exists in repository root assets directory.
- OpenCV validation succeeded: `cap.isOpened()==True` and `frame_count=227` (>=60 requirement).
- Marked the final three Task 11 acceptance leaf checkboxes to `[x]` in plan.