fix(ui): make the advanced prompt editor scrollable

[floze-the-genius]

Description

Makes the Advanced Prompt editor usable when its content is taller than the available macOS window.

The sheet now has a height cap and two explicit regions:

• a vertically scrollable editor body
• a fixed action footer containing Reset, Cancel, and Save

Keeping the actions outside the scroll view means Save and Cancel remain reachable even when the embedded AppKit prompt editor consumes its own scroll gestures.

Type of Change

• Bug fix
• New feature
• Breaking change
• Chore
• Documentation update

Related Issue or Discussion

Closes #633.

Testing

• Tested on Intel Mac
• Tested on Apple Silicon Mac
• Tested on macOS version: 26.4.1
• Ran linter in CI: swiftlint --strict --config .swiftlint.yml Sources
• Ran formatter locally: swiftformat --config .swiftformat Sources/Fluid/UI/AISettingsView+AdvancedSettings.swift
• Ran syntax validation: swiftc -parse Sources/Fluid/UI/AISettingsView+AdvancedSettings.swift
• Built the app in GitHub Actions

Screenshots / Video

The Advanced Prompt editor running from the ad-hoc GitHub Actions artifact for
head SHA 47368957eb4463955f1b45ec83c8c64b1ec23d3f. The editor content is
scrollable while Cancel and Save remain visible in the fixed footer.

• No UI/visual changes; screenshots/video are not applicable.

Notes

• git diff --check passes.
• The refreshed CI archive and full FluidVoice build completed successfully.
• The follow-up keeps the action buttons outside the nested prompt editor scroll view in response to automated review.

[github-actions]

The PR Policy check is blocking this PR because required template information is missing.

Please update the PR description with:

• Screenshots / Video

Visual files detected:

• Sources/Fluid/UI/AISettingsView+AdvancedSettings.swift

Screenshots or video are required for UI, UX, settings, onboarding, overlay, menu bar, or visual behavior changes. If this PR has no visual changes, check the no-visual-change box in the template.

If this remains incomplete for 48 hours after opening, the PR may be closed.

[greptile-apps]

Greptile Summary

This PR makes the Advanced Prompt editor sheet scrollable by wrapping the editable content in a SwiftUI ScrollView while pinning the Save/Cancel buttons below a Divider at the bottom of the sheet, preventing them from being clipped on smaller screens.

• The outer VStack changes from spacing: 14 to spacing: 0; .padding() is redistributed to the inner content VStack and the action button row individually, preserving visual spacing inside the scroll area.
• The sheet frame gains idealHeight: 700, maxHeight: 720, capping the window height and triggering the outer scroll when content overflows.

Confidence Score: 5/5

The change is narrowly scoped — only the layout structure of promptEditorSheet is touched — and the existing editor, validation, and save/cancel logic are unmodified.

The restructuring is mechanical (indent-in under ScrollView, move buttons outside), no logic changes are introduced, and the frame constraints are sensible. No regressions to existing behaviour were identified.

No files require special attention.

_{Reviews (2): Last reviewed commit: "fix(ui): keep prompt editor actions visi..." | Re-trigger Greptile}