fix(desktop): restore maximized window dragged by the caption

[HandSonic]

Related issue

N/A — defect found by reviewing the #2711 desktop chrome series; described below.

Summary

Dragging the custom Windows title bar while the window is maximized kept calling setLocation against the maximized bounds: the window stayed pinned instead of following the pointer until the user restored it by double-clicking. The drag handler now clears MAXIMIZED_BOTH on the first drag event and re-anchors the window under the pointer at the same relative position (new pure restoredDragOrigin), matching native Windows behavior.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• mvn -pl chat2db-community-jcef -am test -Dmaven.test.skip=false: WindowsCommunityWindowChromeTest 7/7 green, incl. 2 new cases (proportional re-anchor; center fallback when the maximized size is unknown).
• Fork CI green: fix(desktop): restore maximized window dragged by the caption HandSonic/Chat2DB#45.

Risk and compatibility

• Public API or stored data: N/A.
• Database or driver compatibility: N/A.
• Network, privacy, or security: N/A.
• Community / Local / Pro boundary: Windows community chrome only.
• Backward compatibility: non-maximized dragging unchanged (draggedWindowLocation untouched).

Reviewer map

• Start here: BrowserWindowDragHandler.mouseDragged + restoredDragOrigin in WindowsCommunityWindowChrome.
• Failure condition: if the frame size updates asynchronously after un-maximizing, the anchor degrades gracefully to the stale-size proportion.
• Rollback or disable path: revert single commit.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: substantial — fix and tests drafted with AI assistance, verified locally.