Vault page: hide empty Access/Store request sections, collapse the inventory sections, and explain grants vs. trust

Three small refinements to the owner vault page (also applied to the operator's per-subject view where the same sections render).

Problem

• The Access requests and Store requests tables are always rendered, but are empty in the common case -- two permanently-empty tables that are pure noise.
• Active grants (per-item read/write grants) and Consumer access (standing per-kind trust) look almost identical but mean different things, with nothing explaining the difference.

Changes

• Render the Access/Store request sections only when there is something pending (inbox-style): the table helpers return NULL when empty and the callers omit the whole section. Both render paths (owner overview + operator per-subject view).
• Collapse the Active grants and Consumer access sections by default -- they are inventory, not action items.
• Add a one-line description above each of those two tables clarifying per-item grants vs per-kind trust.

Tests / i18n

A functional test asserts the request sections are omitted on an empty vault while the inventory sections remain. French translations added for the new description strings.