feat: Add relative mouse mode (#13928)

* feat: Add relative mouse mode

- Add "Relative Mouse Mode" toggle in desktop toolbar and bind to InputModel
- Implement relative mouse movement path: Flutter pointer deltas -> `type: move_relative` -> new `MOUSE_TYPE_MOVE_RELATIVE` in Rust
- In server input service, simulate relative movement via Enigo and keep latest cursor position in sync
- Track pointer-lock center in Flutter (local widget + screen coordinates) and re-center OS cursor after each relative move
- Update pointer-lock center on window move/resize/restore/maximize and when remote display geometry changes
- Hide local cursor when relative mouse mode is active (both Flutter cursor and OS cursor), restore on leave/disable
- On Windows, clip OS cursor to the window rect while in relative mode and release clip when leaving/turning off
- Implement platform helpers: `get_cursor_pos`, `set_cursor_pos`, `show_cursor`, `clip_cursor` (no-op clip/hide on Linux for now)
- Add keyboard shortcut Ctrl+Alt+Shift+M to toggle relative mode (enabled by default, works on all platforms)
- Remove `enable-relative-mouse-shortcut` config option - shortcut is now always available when keyboard permission is granted
- Handle window blur/focus/minimize events to properly release/restore cursor constraints
- Add MOUSE_TYPE_MASK constant and unit tests for mouse event constants

Note: Relative mouse mode state is NOT persisted to config (session-only).
Note: On Linux, show_cursor and clip_cursor are no-ops; cursor hiding is handled by Flutter side.

Signed-off-by: fufesou <linlong1266@gmail.com>

* feat(mouse): relative mouse mode, exit hint

Signed-off-by: fufesou <linlong1266@gmail.com>

* refact(relative mouse): shortcut

Signed-off-by: fufesou <linlong1266@gmail.com>

---------

Signed-off-by: fufesou <linlong1266@gmail.com>

src/platform/windows.rs

@@ -116,12 +116,51 @@ pub fn get_focused_display(displays: Vec<DisplayInfo>) -> Option<usize> {
 
 pub fn get_cursor_pos() -> Option<(i32, i32)> {
     unsafe {
-        #[allow(invalid_value)]
-        let mut out = mem::MaybeUninit::uninit().assume_init();
-        if GetCursorPos(&mut out) == FALSE {
+        let mut out = mem::MaybeUninit::<POINT>::uninit();
+        if GetCursorPos(out.as_mut_ptr()) == FALSE {
             return None;
         }
-        return Some((out.x, out.y));
+        let out = out.assume_init();
+        Some((out.x, out.y))
+    }
+}
+
+pub fn set_cursor_pos(x: i32, y: i32) -> bool {
+    unsafe {
+        if SetCursorPos(x, y) == FALSE {
+            let err = GetLastError();
+            log::warn!("SetCursorPos failed: x={}, y={}, error_code={}", x, y, err);
+            return false;
+        }
+        true
+    }
+}
+
+/// Clip cursor to a rectangle. Pass None to unclip.
+pub fn clip_cursor(rect: Option<(i32, i32, i32, i32)>) -> bool {
+    unsafe {
+        let result = match rect {
+            Some((left, top, right, bottom)) => {
+                let r = RECT {
+                    left,
+                    top,
+                    right,
+                    bottom,
+                };
+                ClipCursor(&r)
+            }
+            None => ClipCursor(std::ptr::null()),
+        };
+        if result == FALSE {
+            let err = GetLastError();
+            log::warn!(
+                "ClipCursor failed: rect={:?}, error_code={}",
+                rect,
+                err
+            );
+            return false;
+        }
+        true
     }
 }