fix(bindings): persist Quick Access reorders atomically

[postigodev]

Summary

Quick Access drag-to-reorder currently persists the new favorite order by saving each binding one at a time.

Current behavior

The frontend computes the reordered favorite list, updates local state optimistically, then loops through every favorite and calls bindingsSave() separately with the new favorite_order.

If one of those writes fails after earlier writes succeeded, the frontend restores its previous in-memory order while the persisted bindings.json may already contain a partial reorder.

Expected outcome

Persist a Quick Access reorder as one backend operation and one durable store replacement.

Acceptance criteria

• expose a focused backend operation for reordering favorites (or equivalently saving the complete normalized order atomically)
• validate that all referenced binding IDs exist and that the requested favorite order is valid
• normalize favorite orders to a contiguous sequence
• write bindings.json once using the existing temporary-file/replace path
• update the frontend to call the atomic reorder operation instead of saving favorites in a loop
• on failure, persisted and in-memory state remain consistent
• add regression coverage for reorder normalization and invalid/missing IDs

Constraints

• do not replace the existing safe binding-store write mechanism
• keep normal create/edit binding operations independent from reorder semantics

Likely files

• crates/core/src/bindings.rs
• apps/tauri/src-tauri/src/commands.rs
• apps/tauri/src/api.ts
• apps/tauri/src/main.ts