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

iosApp/iosApp.xcodeproj/project.pbxproj

@@ -230,6 +230,12 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
+				OTHER_LDFLAGS = (
+					"$(inherited)",
+					"-lsqlite3",
+					"-Wl,-U,_sqlite3_enable_load_extension",
+					"-Wl,-U,_sqlite3_load_extension",
+				);
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
@@ -388,6 +394,12 @@
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
+				OTHER_LDFLAGS = (
+					"$(inherited)",
+					"-lsqlite3",
+					"-Wl,-U,_sqlite3_enable_load_extension",
+					"-Wl,-U,_sqlite3_load_extension",
+				);
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2";