feat(sync): render attachment-aware review output

[ctawiah]

Context

Tool and skill changes are reviewed as part of the variation that references them. This layer updates the terminal output so users can see that relationship clearly and understand exactly what will change before confirming a sync.

What changes

• Groups sync output by project, config, and variation.
• Shows every tool and skill as a separate child of its variation instead of combining several attachments into one diff.
• Labels stable keys consistently so names and identifiers are easy to distinguish.
• Uses indentation to make the resource hierarchy clear in the terminal.
• Renders attachment content in a readable form instead of showing raw API JSON.
• Keeps side-by-side diffs focused on the lines around a change.
• Separates variation content changes from tool and skill content changes.
• Avoids showing an empty-field difference when omitted maps are semantically the same as empty maps returned by LaunchDarkly.

Review focus

• Is it clear which config and variation own each attachment?
• Can a user distinguish several tools or skills attached to the same variation?
• Are the side-by-side diffs concise without hiding useful context?
• Do no-change variations avoid displaying misleading content differences?
• Does the output remain readable in both interactive and non-interactive terminals?

Verification

• go test ./internal/sync/prompt
• go test ./...
• git diff --check

Related changes

Review the stack in this order:

1. Confirm destructive watch actions
2. Guarantee prompt fingerprint convergence
3. Add searchable attachment API foundations
4. Reconcile variation attachments
5. Attach tools and skills to variations
6. Render attachment-aware review output
7. Safely clean unreferenced attachments
8. Persist sync manifests in LaunchDarkly