Feature request: Separate color configuration for action button states

Problem

Currently, the action buttons (boost, favorite, bookmark) use the same tint color as links. This creates two issues:

1. Hard to distinguish active states: The boost button only changes color (icon isn't filled), making it difficult to quickly see if a post has already been boosted
2. No flexibility: Users who prefer a specific link color are forced to use that same color for action button states

Proposed Solution

Allow users to configure action button colors separately from the link tint color. Options could include:

• A dedicated color picker for "active action button" state
• Or: Use filled icons for active states (boost, favorite already boosted/favorited)
• Or: A high-contrast default that differs from the link color

Why This Matters (Accessibility)

Quick visual scanning of a timeline to identify already-interacted posts is a common use case. The current subtle color-only change (without filled icons) requires extra cognitive effort, especially for users with color vision differences.

Environment

• IceCubesApp (iOS/macOS)

No files or tests are named. Start by locating the SwiftUI action-button views and the settings that provide the link tint, then compare boost, favorite, and bookmark active-state rendering on iOS and macOS. Done means the chosen design clearly distinguishes active states and provides the requested separate configuration or visual treatment without relying only on color.