feat(ui): wire filter + sort into the slots view

[thewrz]

Parent epic: #194 · Needs: #196 (filter), #197 (sort).

Scope

Slot manager (src/ui/slot_manager.rs) gains the shared search bar with TypeToFilter activation and the sort chip with SlotSortKey (default SlotNumber ↑). Filter matches the assigned sound's customized name, file name, and tag/folder.

Invariant: sorting reorders the list rendering only — slot numbers and assignments stay attached to their rows; it never remaps which sound lives in which slot.

Acceptance

• Typing on the slots view filters rows immediately; empty slots behavior defined (hidden while filtering, shown otherwise).
• Sort by every SlotSortKey; persisted as sort_prefs["slots"].
• App-state tests for filter/sort composition on slot rows.

Design: docs/superpowers/specs/2026-07-06-list-controls-design.md