Persist exchange rates, selected currencies, and price source via SQLDelight

Adds a SQLDelight-backed AppDatabase (Android, Desktop, iOS/macOS) so the
converter survives restarts: the last-known rates per price source, the
user's selected fiat currencies (with order preserved), and the last-used
price source all reload before the first network fetch completes. Web isn't
a shipped platform and SQLDelight's driver there needs a worker plus a wasm
sqlite binary, so it gets a lighter localStorage-backed implementation of
the same store interfaces instead.

Android needs an app Context for its driver, wired via a new
SatsPriceApplication. iOS/macOS need libsqlite3 linked explicitly (Swift's
autolinking only covers Shared.framework itself, not its C library
dependencies), plus two extension-loading symbols marked optional since
macOS's system sqlite build omits them.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QpjMKWGoiT5aJBzhxvXkwp

androidApp/src/main/AndroidManifest.xml

@@ -2,6 +2,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
     <application
+            android:name=".SatsPriceApplication"
             android:allowBackup="true"
             android:icon="@mipmap/ic_launcher"
             android:label="@string/app_name"

androidApp/src/main/kotlin/xyz/tyiu/satsprice/SatsPriceApplication.kt

@@ -0,0 +1,11 @@
+package xyz.tyiu.satsprice
+
+import android.app.Application
+import xyz.tyiu.satsprice.data.db.initAndroidContext
+
+class SatsPriceApplication : Application() {
+    override fun onCreate() {
+        super.onCreate()
+        initAndroidContext(this)
+    }
+}