CALANAIS ADVERSARIAL REPRODUCIBILITY LAYER v3

New files:
- pythagorean_base_rate_v3.py / pythagorean_base_rate_results_v3.json
- directional_partition_null_v3.csv
- endpoint_position_sensitivity_v3.csv
- scorpius_star_inputs_v3.csv / scorpius_all_pairings_v3.csv / scorpius_rival_audit_v3.py
- PRE_CALANAIS_EXTERNAL_CHRONOLOGY_v3.txt
- ADVERSARIAL_LAYER_v3_RESULTS.json

Interpretive rule: these calibrations are not multiplied. The generic best-triple null deliberately demotes the Pythagorean rank as standalone evidence; the prior-specific template and directional bracket quantify the channels relevant after the external pre-Calanais target freeze. Endpoint sensitivity is a phase boundary and cannot be used for endpoint retuning.
