Power Display: Remove hardcoded flyout position / allow customized placement

### Microsoft PowerToys version

0.99.1

### Installation method

WinGet

### Area(s) with issue?

Power Display

### Steps to reproduce

Click the systray icon to open flyout

### ✔️ Expected Behavior

At minimum, flyout should appear next to its location in the systray, without hardcoding a bottom right position. Ideally, the position should be adjustable and persistent.

### ❌ Actual Behavior

Flyout appears on the far end of the screen with no regard to taskbar orientation:

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### Additional Information

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### Other Software

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Start by locating the Power Display flyout implementation and reproduce the issue by opening it from the systray with different taskbar orientations. Trace how its position is selected. Done means the flyout opens beside its systray location instead of a hardcoded bottom-right position, with any supported placement setting persisting.

Written by the indexing model from the issue text.