Function install_pack 

pub async fn install_pack(
    db: &SqlitePool,
    manifest: &PackManifest,
    dry_run: bool,
) -> Result<InstallPackOutcome, CoreError>

Install (or dry-run preview) every rule in a fetched pack manifest.

Idempotency / supersede (roadmap §5 step 6): a rule already present at this exact pack:<id>@<version> is left untouched; a rule present at a different version of the same pack is deleted and replaced (version supersede), keyed on its pack-rule:<ruleId> tag. All writes happen in one transaction; the store’s updated_at is bumped so the cross-repo starter index rebuilds lazily on next recall.