Custom tooltip composable slot API

[aldefy]

Problem

The built-in tooltip layout (title, description, CTA in a column) doesn't always match client design systems. Designers want full control over tooltip composition — custom CTA shapes, different text layouts, brand-specific styling.

Example: Client's Figma shows a full-width green pill CTA button with no card background, but the library renders a fixed-size blue rounded CTA in a card.

Proposed Solution

Add a customTooltip slot to CoachmarkHost or CoachmarkTarget:

CoachmarkHost(
    controller = controller,
    customTooltip = { target, currentStep, totalSteps, onNext, onDismiss ->
        // Full composable freedom
        Column {
            Text(target.title, style = MaterialTheme.typography.headlineSmall)
            Text(target.description)
            Button(
                onClick = onNext,
                shape = RoundedCornerShape(50),
                modifier = Modifier.fillMaxWidth(),
            ) {
                Text(target.ctaText)
            }
        }
    },
)

When customTooltip is provided, skip the default CoachmarkTooltip rendering but keep connector, cutout, and scrim behavior.

Why This Matters

Client feedback: "Composition off" — the built-in tooltip layout cannot match their Figma designs closely enough. This is the most requested capability for production adoption.