fix(core): normalize favorite order after binding deletion

[huyua9]

What changed

• compact persisted favorite_order values after deleting a binding
• preserve the existing favorite ordering while assigning contiguous positions
• update the binding persistence regression test to cover the compacted order

Why

Deleting the first Quick Access favorite left the remaining favorite at order 2, creating a gap in persisted ordering.

Validation

• cargo fmt --all -- --check
• cargo test -p desk_remote_core (14 passed)
• git diff origin/main...HEAD --check

AI-assisted; the change is limited to crates/core/src/bindings.rs.

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