🎨 Palette: Improve IconButton accessibility touch targets

[yuga-hashimoto]

💡 What: Moved explicit visual size constraints (Modifier.size(24.dp)) from interactive IconButton containers to their inner decorative Icon elements across MainActivity and ChatActivity.
🎯 Why: Setting a small explicit size on an IconButton component inadvertently overrides Jetpack Compose's automatic minimum touch target enlargement, breaking Android accessibility guidelines (48x48dp minimum). By applying the size modifier to the inner Icon, the visual design remains identical while allowing the IconButton to seamlessly maintain a large, accessible hit area.
📸 Before/After: Visuals are identical, but tap targets for settings, refresh, and stop buttons are significantly easier to hit, especially for users with motor impairments.
♿ Accessibility: Ensures all interactive icon buttons meet the minimum touch target standard (48x48dp).

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PR created automatically by Jules for task 1391468699217276056 started by @yuga-hashimoto

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