fix(automation): isolate managed skill test exports

[ScriptedAlchemy]

Summary

• prevent non-default TraceDecay test profiles from reconciling user-global managed skills
• preserve Codex and Claude skill exports during automation integration tests
• cover default versus isolated profile roots

Verification

• cargo test-all — 4663 passed, 2 skipped
• cargo test --test automation_runner_test skill_writer --quiet — 20 passed
• dogfood install and tracedecay doctor — Codex/Claude materializations in sync
• repeated skill-writer test preserved live managed skill files

[changeset-bot]

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Latest commit: b220a79

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