Vue adapter + wire the loading controller into the modal

[pringelmann]

Context

Controller subtask ships a standalone UnifiedSearchController (plain TS, no Vue, unit-tested), but nothing consumes it yet. This tracks the wiring.

Scope

Four parts:

• Controller filter pass-through: accept per-category since / until / person / extraQueries
• useUnifiedSearch() composable: a thin reactive adapter around the controller, torn down via dispose() on unmount.
• Rewire UnifiedSearchModal.vue to consume new controller
• dev toggle to delay/fail a provider (to demo the blocked/failed states)