fix(macos): accept docked clamshell power evidence

[tcconnally]

Summary

• Accept verified docked-clamshell power evidence for MacBooks connected to external displays.
• Record a sanitized external_display_observed marker from system_profiler SPDisplaysDataType.
• Keep open-lid evidence valid and fail closed when neither open-lid nor external-display clamshell evidence is present.

Reproduction

The live M5 capture ran on AC power with 26 AC/assertion samples, but the MacBook lid was intentionally closed in a dual-monitor dock. The analyzer reported lid_open_samples=0 and blocked power_sleep_evidence even though the intended supported operating mode was docked clamshell.

Verification

• Added a docked-clamshell parser/gate regression test.
• Added fail-closed behavior for missing external-display evidence.
• python3 tests/run_all.py: PASS on the exact candidate.
• python3 -m compileall -q hyperwall scripts tests: PASS.
• git diff --check: PASS.

This changes evidence policy only; it does not promote any cell count or claim native media qualification.