Reapply shortcuts when restoring current defaults

[arhxam]

Summary

• always reload registered shortcuts after restoring a default shortcut scheme
• clear all active shortcut overrides before selecting the requested scheme
• preserve the existing cancel flow and snap-area reset behavior

Fixes #1119.

Previously, selecting the already-active scheme removed persisted overrides but skipped the changeDefaults notification. The shortcut binder therefore kept stale or conflicting bindings until Rectangle restarted.

Verification

• ShortcutDefaultsRestoreTests: 2/2 passing for same-scheme and changed-scheme resets
• full RectangleTests: 207 tests run; the same 22 pre-existing assertions fail as on main, confined to ActiveSideSplitRatiosCooperativeTests, CooperativeCornerResizeTests, and HalfSplitCornerCalculationTests
• git diff --check origin/main...HEAD

AI assistance

AI tooling assisted with investigation, implementation, and test generation. The final diff passed independent specification and code-quality reviews and was verified locally.

[rxhanson]

Thanks for contributing! All of these PRs look good, I'll just spend some time manually testing prior to merging.