fix(desktop): keep line comment popovers above session review accordion

[OpeOginni]

Issue for this PR

Closes #15098

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Stopped the accordion wrappers from clipping overflowing content, and increased the open comment layer (z-index) so the popup can sit above nearby UI.

How did you verify your code works?

Tested locally with my dev run of the desktop

Screenshots / recordings

Screen.Recording.2026-02-26.at.16.11.55.mov

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Hey! Your PR title fix(desktop/ui): keep line comment popovers above session review accordion doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.