refactor: improve toast apis and internals

[ovitrif]

This PR refactors the toast system to improve architecture, API consistency, and localization.

Changes

Architecture

• Replace ToastEventBus singleton with injectable Toaster using SharedFlow
• Add ToastText sealed interface with Resource, Literal, and Parameterized subtypes
• Inject Toaster in MainActivity via Hilt, provide via LocalToaster
• Rename ToastQueueManager → ToastQueue

API Consolidation

• Factory constructors: ToastText(resId), ToastText(string), ToastText(resId, params)
• Composable parameter pattern: toaster: Toaster = LocalToaster.current
• Remove app.toast() API, use toaster.*() directly
• Rename: description → body, visibilityTime → duration, warning() → warn()

String Replacement

• ToastText.Parameterized(resId, mapOf("key" to "value")) replaces {key} in strings

Localization

• Migrate all hardcoded toast strings to string resources
• Add ToastText.asString() extensions (composable and Context)

Cleanup

• Rename ToastView → ToastContent, ToastOverlay → ToastHost

Usage

// Simple
toaster.success(title = ToastText(R.string.success))

// With body
toaster.error(
    title = ToastText(R.string.error_title),
    body = ToastText(R.string.error_body),
)

// With string replacement
toaster.warn(
    body = ToastText(R.string.amount_exceeded, mapOf("amount" to "1000")),
)

// In composables
@Composable
fun MyScreen(toaster: Toaster = LocalToaster.current) {
    Button(onClick = { toaster.success(ToastText(R.string.done)) }) { ... }
}

QA Notes

1. Toast Functionality: Trigger various toast types, verify styling and auto-dismiss
2. Queue Behavior: Trigger multiple toasts rapidly, verify sequential display
3. Drag Interactions: Drag toast to pause timer, release to resume
4. Localization: Change device language, verify translated messages