Under Increase Contrast the AI suggestion ghost is drawn exactly like typed text

## What happens

With Increase Contrast or Reduce Transparency on, the ghost text is drawn exactly like the user's own text.

- `SuggestionAppearance.demandsOpaqueGhost` is `increasesContrast || reducesTransparency` (`Sources/UttrflowUX/SuggestionPresentation.swift:27`).
- Under it, `opacity` becomes `opaqueGhostOpacity = 1.0` (`:65`, `:126`).
- `SuggestionView.inlineLine` distinguishes the ghost by opacity alone: `.primary.opacity(presentation.opacity)`, same font, no italic, underline or tint (`Sources/Uttrflow/Suggestion/SuggestionView.swift:56-59`, `:95-105`).

So at 1.0 the suggestion is indistinguishable from typed text. A user who turned on Increase Contrast because faint grey is hard to read now cannot tell what they wrote from what is offered.

## Why it matters

Users who rely on Increase Contrast are exactly the ones who cannot use a faint cue. Removing the only cue does not help them. They may send or run a line believing it was already typed.

## How to reproduce

Turn on System Settings → Accessibility → Display → Increase Contrast and trigger an AI suggestion. The offered text looks like typed text. `SuggestionPresentationTests` would show `opacity == 1.0` with no other style difference.

## Acceptance criteria

- Under Increase Contrast and Reduce Transparency the ghost stays legible and still looks different from typed text by something other than opacity: an underline, a dotted underline, an accent colour meeting 4.5:1, or a solid high-contrast backing.
- `SuggestionPresentation` exposes that style so it is unit-tested in `Tests/UttrflowUXTests`.

Start with Sources/UttrflowUX/SuggestionPresentation.swift and Sources/UttrflowUX/Suggestion/SuggestionView.swift, then inspect SuggestionPresentationTests in Tests/UttrflowUXTests. Verify the Increase Contrast and Reduce Transparency paths, expose a non-opacity distinction for the ghost, and add unit coverage showing it remains legible and visually different from typed text.

Written by the indexing model from the issue text.