Add guarded Zenodo sandbox write commands

[edithatogo]

Summary

• expose guarded Zenodo sandbox draft creation, metadata, and file workflows
• add dry-run-first lifecycle commands with exact publish and discard confirmations
• document sandbox-only scope and long-term repository provider candidates
• restore Conductor project context index

Validation

• go test -p 1 ./internal/cli ./internal/zenodopublish ./internal/zenodotransfer
• go vet -p 1 ./internal/cli ./internal/zenodopublish ./internal/zenodotransfer
• go run ./tools/checkstubs
• go run ./tools/checkfeaturematrix
• go run ./tools/checkregistries
• mkdocs build --strict

Production Zenodo and MCP writes remain unavailable.

[gemini-code-assist]

Caution

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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