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

[jvsena42]

some improvements like constant extractions implemented in #914

[pwltr]

I tested on device, works as described, except it did not seem to update price for me automatically (waited ~30minutes). Only after I tapped the widget did it reload. Still don't know anything about Kotlin so won't review code.

EDIT: have seen it update now

[claude]

Code review

Found 2 issues: 1 CLAUDE.md violation and 1 bug.

[claude]

CLAUDE.md violation — The inner private composable must be named Content per CLAUDE.md:

ALWAYS split screen composables into parent accepting viewmodel + inner private child accepting state and callbacks Content()

The codebase consistently uses the literal name Content for the private inner child (e.g. ContactsScreen.kt, ProfileScreen.kt). This should be renamed from PriceConfigContent to Content.

Suggested change

	private fun PriceConfigContent(
	private fun Content(

[claude]

Bug — viewModel.init() is called unconditionally in onCreate, which runs again on any configuration change (locale switch, font size adjustment, dark/light mode toggle) — not just rotation. At that point the widget hasn't been saved to the DataStore yet, so preferencesStore.getEntry(appWidgetId) returns null and the user's in-progress selections are silently reset to PricePreferences().

Fix: guard with savedInstanceState == null so init only runs on the first launch:

Suggested change

	viewModel.init(appWidgetId, type)
	if (savedInstanceState == null) viewModel.init(appWidgetId, type)