fix(sync): safely clean unreferenced attachments

[ctawiah]

Context

A local tool or skill file is no longer needed after the final synchronized variation stops referencing it. This layer completes the attachment lifecycle by finding those files and asking before removing them. It applies the same behavior to normal syncs and watch mode.

What changes

• Finds local tool and skill files that are not referenced by any synchronized variation.
• Prompts before deleting an unreferenced file.
• Treats --yes as confirmation for attachment cleanup along with the rest of the sync.
• Removes confirmed files as one transaction so a failed deletion can be rolled back safely.
• Rejects unexpected paths, duplicate selections, non-regular files, and symbolic links before deleting anything.
• Runs cleanup only after a successful sync or after confirming that there are no resource changes to apply.
• Watches all managed source files directly instead of rebuilding the watch scope from project directories.
• Passes watcher state into each sync run explicitly.

This cleanup only removes local files. It does not delete tools or skills from LaunchDarkly.

Review focus

• Does cleanup wait until the final local reference has been removed?
• Are interactive confirmation and --yes handled consistently?
• Can a partial filesystem failure leave a deleted attachment file behind?
• Does watch mode run the same cleanup and confirmation flow as a normal sync?
• Are path and symbolic-link checks applied before any file is moved or removed?

Verification

• go test ./internal/sync/local ./internal/sync/prompt ./internal/sync/detach
• go test ./...
• go vet ./internal/sync/... ./cmd/sync
• 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

---

Note

Overview
Adds orphaned local attachment cleanup to the sync prompt flow: after a successful sync (or when the plan has no changes and the user declines apply), the CLI finds managed tools/*.json and skills/*.md files that no variation still references, lists them, and deletes only after interactive confirmation or --yes (with a second reference check right before delete).

The local store gains OrphanedAttachments and DeleteAttachments, using staged renames plus path/symlink/regular-file validation. commitDeletions now treats the staged rename as the commit point and cleans up backups best-effort (no partial rollback on backup removal failure).

Watch mode passes the file watcher into each sync explicitly, and SourceFiles includes all files under project subtrees in .launchdarkly (not just variation wrappers) so attachment edits trigger sync. Store.ProjectKeys is removed.

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