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

shared/src/jvmMain/kotlin/xyz/tyiu/satsprice/data/db/SqlDelightStores.jvm.kt

@@ -0,0 +1,20 @@
+package xyz.tyiu.satsprice.data.db
+
+import app.cash.sqldelight.driver.jdbc.sqlite.JdbcSqliteDriver
+import xyz.tyiu.satsprice.db.AppDatabase
+import java.io.File
+
+private val database: AppDatabase by lazy {
+    val appDir = File(System.getProperty("user.home"), ".sats-price").apply { mkdirs() }
+    val databaseFile = File(appDir, "sats-price.db")
+    val isNewDatabase = !databaseFile.exists()
+    val driver = JdbcSqliteDriver("jdbc:sqlite:${databaseFile.absolutePath}")
+    if (isNewDatabase) {
+        AppDatabase.Schema.create(driver)
+    }
+    AppDatabase(driver)
+}
+
+actual fun createExchangeRateStore(): ExchangeRateStore = SqlDelightExchangeRateStore(database)
+actual fun createSelectedCurrenciesStore(): SelectedCurrenciesStore = SqlDelightSelectedCurrenciesStore(database)
+actual fun createSelectedSourceStore(): SelectedSourceStore = SqlDelightSelectedSourceStore(database)