feat: stage managed skill consolidations

[ScriptedAlchemy]

Summary

• add managed-skill overlap evidence for skill_writer consolidation candidates
• stage merge/archive consolidation proposals behind human approval while preserving skill content
• validate ids, base checksums, pending updates, user-authored exemptions, and pinned-skill exemptions

Verification

• CARGO_TARGET_DIR="$HOME/.cache/tracedecay-targets/hermes-r6-consolidation" cargo check --workspace
• CARGO_TARGET_DIR="$HOME/.cache/tracedecay-targets/hermes-r6-consolidation" cargo test --workspace overlap
• CARGO_TARGET_DIR="$HOME/.cache/tracedecay-targets/hermes-r6-consolidation" cargo test --workspace staged_managed_skill_archive
• CARGO_TARGET_DIR="$HOME/.cache/tracedecay-targets/hermes-r6-consolidation" cargo test --workspace skill_writer
• cargo fmt --check
• git diff --check
• scripts/check-conventional-commits.sh origin/master..HEAD

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Latest commit: 3b5e747

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