Restore prediction margins after landscape rotation

[damonbayer]

Prediction rows can retain the landscape margin after returning to portrait. Remove the explicit separator-to-content-margin assignments from prediction input rows, chart cell configuration, and the legacy potential carb-entry cell. UIKit then updates margins for the current safe area and readable width through the existing constraints.

Addresses #2477. The related #1610 verification is summarized below. Companion fixes: LoopKit #645 and RileyLinkKit #22.

Before and after

Predicted Glucose in the full Loop app, on iPhone 17 Pro simulator with iOS 26.5, after portrait → landscape → portrait. The original rows retain the landscape inset; the fixed rows restore their portrait alignment. The app was unconfigured, so the graph is intentionally empty. Capture details and baseline revisions.

Before: next-dev	After: this change

Validation and #1610 coverage

• Full LoopWorkspace simulator build passed with Xcode 27.
• Predicted Glucose passed the rotation round trip and opening in landscape before returning to portrait.
• Production Carbohydrates storyboard/cell fixtures with synthetic values restored label bounds within 0.5 pt; no additional Carbohydrates change was needed.
• Production Therapy Settings views showed the grouped background in both landscape safe areas in a synthetic fixture. The original physical-device-only report still needs physical-device confirmation.
• The Bolus comment remains unresolved: its explicit portrait restriction is unchanged. This PR does not claim to close all of Various Screen Rotation Issues in loop-dev #1610.
• Source audit covered every screen family and shared pump/CGM/service/onboarding components. Connected-device screens were not all exercised live.
• No new test sources or test-project references are included.

Companion PRs

• Loop #2573
• LoopKit #645
• RileyLinkKit #22