Propagate cache hygiene to generated packages

[diegohb]

What to build

Packages produced by the packager and publisher must inherit the cache behavior from this suite, self-scoped only.

• the generated installer template prunes its own package's @latest, @<running version>, and untagged cache copies on install (same best-effort, warn-and-continue semantics as the suite)
• the generated CLI template exposes a self-only clear-cache subcommand; it must not offer --package or --all
• the generated load-time plugin advisory suggests bunx <pkg> clear-cache for a partial cache artifact instead of only describing manual removal
• the conformance checklist gains an item covering this cache hygiene
• packager/publisher instructions require the generated output to include it

The load-time hook itself still never deletes the cache (ADR-0007: deletion races in-flight installs); only the CLI does.

Acceptance criteria

• Installer template prunes self cache copies on install, including no-op, warn-and-continue
• Generated CLI exposes self-only clear-cache with no --package/--all
• Plugin-local advisory names bunx <pkg> clear-cache
• Conformance checklist item added and referenced by the auditor
• Packager/publisher instructions updated so generated packages carry it
• Regression coverage for the template behavior (or a documented assertion) in the suite's test harness

Blocked by

• Prune stale cache copies when installing #12 Prune stale cache copies when installing
• Add a clear-cache CLI subcommand #13 Add a clear-cache CLI subcommand