fix(src): defensive try/except in load_track_state for TOMLDecodeError

A malformed state.toml in conductor/tracks/<track>/state.toml (e.g.,
from an interrupted previous run) caused tomllib.load() to raise
TOMLDecodeError, which propagated up and crashed App.__init__
during init_state() -> _load_active_project() -> _refresh_from_project()
-> get_all_tracks() -> load_track_state().

This manifested as test failures in tests/test_layout_reorganization.py,
tests/test_auto_slices.py, tests/test_hooks.py, and the tier-3-live_gui
batch (all triggered by the same malformed mcp_architecture_refactor_20260606
state.toml).

The fix wraps tomllib.load() in a try/except for (OSError,
tomllib.TOMLDecodeError) and returns None (matching the file-not-found
behavior). This is consistent with the data-oriented convention:
corrupt state is a recoverable failure, not a programmer error.

Tests verified:
- tests/test_track_state_persistence.py (1 test) PASS
- tests/test_layout_reorganization.py (4 tests) PASS
- tests/test_auto_slices.py (3 tests) PASS
- tests/test_hooks.py (3 tests) PASS

src/project_manager.py

@@ -291,7 +291,10 @@ def load_track_state(track_id: str, base_dir: Union[str, Path] = ".") -> Optiona
  from src.models import TrackState
  state_file = paths.get_track_state_dir(track_id, project_path=str(base_dir)) / 'state.toml'
  if not state_file.exists(): return None
- with open(state_file, "rb") as f: data = tomllib.load(f)
+ try:
+  with open(state_file, "rb") as f: data = tomllib.load(f)
+ except (OSError, tomllib.TOMLDecodeError):
+  return None
  return TrackState.from_dict(data)
 
 def load_track_history(track_id: str, base_dir: Union[str, Path] = ".") -> list[str]: