Remove the upgrade confirmation prompt for reversible upgrades #599

The upgrade CLI prompts the user for confirmation. This is unnecessary friction unless the specific upgrade is known to preclude or cause problems for a subsequent downgrade.

Ask

• Skip the upgrade confirmation prompt by default.
• Only prompt (or require an explicit --force / --no-downgrade flag) when the target version makes downgrade lossy or unsupported (e.g. major version bumps with on-disk format changes).
• Maintain a list/table of which upgrades require the prompt so this stays consistent across releases.

Acceptance criteria

• harperdb upgrade (or equivalent) runs without prompting in the common case (minor / patch upgrades that are reversible).
• Cross-major or format-changing upgrades still prompt or require an explicit flag.
• CI automation that runs upgrades doesn't have to pipe yes to it.

Notes

• A test should assert non-interactive upgrade succeeds for the reversible case.

Tracked in Jira: CORE-2980

🤖 Filed by Claude on behalf of Kris.