feat: system widgets foundation + price widget

[jvsena42]

This PR:

1. Adds a Bitcoin Price home screen widget using Jetpack Glance
2. Implements independent widget preferences stored in a separate DataStore
3. Uses WorkManager for periodic background data refresh (15-minute intervals)
4. Includes a configuration Activity for widget settings on click
5. Renders a sparkline chart via Bitmap using Android Canvas API

Description

Introduces the foundation for Android home screen widgets (AppWidgets) using Jetpack Glance, starting with the Price widget. The widget displays enabled trading pairs with price, change percentage, and a line chart — matching the in-app Price widget layout.

The architecture reuses the existing PriceService for data fetching (via a new fetchData(period) overload) while keeping widget preferences completely independent from the in-app widget system through a dedicated AppWidgetPreferencesStore backed by its own DataStore file.

A Glance design system (GlanceTextStyles, GlanceColors) ports the app's typography and color tokens to Glance equivalents, and shared components (GlanceWidgetScaffold, GlanceDataRow) provide consistent widget layouts.

Preview

Screen_recording_20260421_153032.webm

QA Notes

1. Long-press the home screen and select "Widgets"
   • Find "Bitcoin Price" in the widget picker
   • Verify the preview shows a price layout with mock data
2. Add the widget to the home screen
   • Verify the configuration screen opens with trading pair and period options
   • Toggle pairs and period, tap Save
   • Verify the widget updates to show selected pairs with price, change %, and sparkline chart
3. Wait 15+ minutes or force-stop and reopen
   • Verify the widget refreshes data via WorkManager
4. Tap the widget
   • Verify it opens the widget settings screen
   • Verify the widget update after saving new preferences
5. Long-press the widget
   • Verify the widget is resizable
   • Verify the chat is hidden if not enough vertical space
6. Verify the OS widget settings are independent from internal app widgets

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test body only - inline comments follow in separate calls

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