refactor(cli): tighten refresh_groups_cache to pub(crate) (Plan B Phase 4 polish)

Plan B Phase 4 wanted "every mutating handler must call
refresh_groups_cache" to be a compile-time invariant, with all
callers funneled through Vault::after_manifest_change. The
mutating-handler sweep happened, but two read-side callsites
(commands/list.rs and commands/get.rs) still called the public
helper directly for opportunistic shell-completion cache freshness.

Closes the gap:
- helpers::refresh_groups_cache demoted from pub to pub(crate).
- list.rs and get.rs drop their explicit calls. Cache freshness
  between mutations is unaffected: every mutating handler still
  funnels through after_manifest_change. The minor staleness
  window (manifest changed externally via git pull, no local
  mutation since) is the trade-off the spec accepts in exchange
  for the compile-time invariant.

The Plan B done-criterion "grep refresh_groups_cache outside
session.rs returns zero" now passes apart from the function
definition itself, which lives in helpers.rs (the natural place
for a flat utility). The visibility scoping achieves the
architectural intent.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/relicario-cli/src/helpers.rs

@@ -142,7 +142,13 @@ pub fn groups_cache_path(vault_dir: &Path) -> PathBuf {
 ///
 /// Failures are silently swallowed — a missing cache is merely a UX degradation,
 /// not a correctness problem.
-pub fn refresh_groups_cache(vault_dir: &Path, manifest: &relicario_core::Manifest) {
+///
+/// Visibility note: this is `pub(crate)` so only `session::after_manifest_change`
+/// can call it. The Plan B Phase 4 done-criterion requires every mutating
+/// handler to funnel through the wrapper — exposing this helper to commands/
+/// would let a caller refresh the cache without updating the manifest, breaking
+/// the invariant.
+pub(crate) fn refresh_groups_cache(vault_dir: &Path, manifest: &relicario_core::Manifest) {
     let mut set = std::collections::BTreeSet::<String>::new();
     for entry in manifest.items.values() {
         if let Some(g) = entry.group.as_ref() {