fix: test_architecture.py — use os.path.dirname(__file__) instead of hardcoded /app for sys.path

fix: test_architecture.py — correct evidence_gate attribute check (gate_type='none' not gate=None), add dinov2 config test, compact formatting

fix: test_architecture.py — add comprehensive ablation tests (no_jepa, no_rollout, no_gate, K variants, loss_fn variants, SIGReg vs VICReg, purist config)

Initial MR-JEPA codebase: architecture, training, evaluation, and tests