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 <[email protected]>

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

Signed-off-by: fufesou <[email protected]>

* refact(relative mouse): shortcut

Signed-off-by: fufesou <[email protected]>

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Signed-off-by: fufesou <[email protected]>

fix click cm audio permission button before auth (#8917)

1. When not authenticated, clicking the audio permission button on the cm will send audio data
2. Keep the cursor position code unchanged, because `show_remote_cursor` is false before auth, so subscription will not happen.
3. Keep the clipboard code unchanged, because the keyboard permission will also be determined in `try_sub_services`. If the clipboard permission is clicked before auth and the keyboard permission is clicked after auth, the clipboard service will not be subscribed.

Signed-off-by: 21pages <[email protected]>