⚡ Performance & 🛡️ Reliability: Async Process Management & Domain Sync Fix

[mx57]

This PR introduces several critical improvements to performance, reliability, and UX:

1. Asynchronous Engine Management: Refactored the core engine control logic (Start/Stop/Switch) to be fully asynchronous. By using await p.WaitForExitAsync() and moving process termination out of the UI thread, we eliminated the noticeable "freezes" (1.5s+ hangs) that occurred when stopping multiple engines (e.g., Zapret + Warp).

2. Full Domain List Synchronization: Fixed a bug where only the target domains were synced to the engine directory. The system now properly synchronizes both the target list (list-general-user.txt) and the exclusion list (list-exclude-user.txt), including legacy markers.

3. I/O Optimization (Debouncing): Implemented a 500ms debounce for settings serialization. This prevents redundant disk writes when the user quickly toggles multiple checkboxes or types in domain lists.

4. AI Selection Performance: Optimized the BanditSelector.Pick method by replacing an $O(N \log N)$ sort with a $O(N)$ linear MaxBy scan for selecting the best strategy.

5. Stability: Updated the update mechanism to await engine shutdown before attempting to overwrite binaries, preventing "file in use" errors during updates.

All changes were verified with the existing test suite (50/50 passed) and a full build targeting Windows. Insight recorded in .jules/bolt.md.

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PR created automatically by Jules for task 5432020798255957903 started by @mx57

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