Remove the upgrade confirmation prompt for reversible upgrades

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.

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Tracked in Jira: [CORE-2980](https://harperdb.atlassian.net/browse/CORE-2980)

🤖 Filed by Claude on behalf of Kris.