[Bug]: Fluent Menu popover does not adjust position for horizontal viewport collision

[jatchison-univerus]

Component

Menu

Package version

3.0.0-rc.1

@microsoft/fast-element version

2.0.0

Environment

System:
    OS: macOS 26.1
    CPU: (10) arm64 Apple M1 Pro
    Memory: 676.00 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Browsers:
    Chrome: 143.0.7499.41
    Firefox: 141.0
    Safari: 26.1

Current Behavior

The menu component lacks horizontal positioning fallbacks. When triggered near the viewport edge, the popover overflows the viewport instead of flipping inline, triggering an unwanted horizontal scrollbar.

Expected Behavior

Should have a horizontal positioning fallbacks (like it does vertically)

Reproduction

https://stackblitz.com/edit/vitejs-vite-6qmsq1jn?file=index.html

Steps to reproduce

Click on button to open menu

Are you reporting an Accessibility issue?

None

Suggested severity

Medium - Has workaround

Products/sites affected

No response

Are you willing to submit a PR to fix?

yes

Validations

• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• The provided reproduction is a minimal reproducible example of the bug.