fix: keep mouse movement smooth across portal edges

[ai-eks]

Summary

• Remove the global mouse/cursor association toggle on every portal crossing.
• Preserve the existing HID event forwarding and original motion deltas for the expected portal-edge feel.
• Read motion deltas only when a portal crossing actually occurs and simplify the callback result to a target point.
• Update the existing display-transition tests for the simplified callback result.

Scope

This PR contains only mouse movement handling and its affected tests. Window capture, tab-change restoration, and persisted window identity changes remain in #7.

Verification

• swift test: 181 tests passed on this branch.
• git diff --check: passed.
• Combined local build with fix: preserve window layout identities across restarts and screen lock #7: 202 tests and release build passed.
• The combined signed app was installed locally and its mouse movement event tap was verified enabled. Subjective smoothness remains a manual check.

[ai-eks]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🎉

Reviewed commit: 6d550d871d

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