Exchange Announcement Banner improvements

[mocodesmo]

---

1. Banner Card Improvements

Before: The banner displayed the full description text, taking up multiple lines.

After:

• Description truncated to one line with ellipsis (...) to keep the banner compact
• Tappable card — wrapped in GestureDetector to open a bottom sheet with full details
• Theme-aware styling:
  • Light mode: Black background (secondary) with white text (onSecondary) — original look
  • Dark mode: Dark surface background with subtle light border (outline at 30% opacity) and light text (onSurface)

---

2. New Bottom Sheet (_AnnouncementBottomSheet)

A new bottom sheet component was added that appears when tapping an announcement:

Structure:

• Uses app's existing BlurredBottomSheet.show() pattern for consistent styling
• Drag handle at the top (40x4px rounded bar)
• Header row with:
  • Info icon (24px, uses onSurface color — black in light mode, white in dark mode)
  • Title text (titleLarge with bold weight)
  • Close button (X icon) on the right
• Scrollable description area with comfortable line height (1.5) and 80% opacity for visual hierarchy

Layout Features:

• maxHeight constraint (80% of screen) to prevent overflow
• SingleChildScrollView wraps the description for very long text
• crossAxisAlignment: center on the header row for proper icon/text alignment
• Uses context.appColors.surface background — adapts to light/dark mode
• Proper padding (24px) and gaps for visual breathing room

---

3. Dark Mode Support

All colors use theme-aware context.appColors values:

Element	Light Mode	Dark Mode
Banner background	secondary (black)	surface (dark)
Banner border	None	outline at 30% opacity
Banner text	onSecondary (white)	onSurface (light)
Bottom sheet background	surface (light)	surface (dark)
Bottom sheet text	onSurface (dark)	onSurface (light)
Icons	Theme-appropriate	Theme-appropriate

---

[mocodesmo]

[FrancisPouliot]

Bottom sheet is a good idea