Add a Compose HTML (DOM) web app and split Compose UI out of :shared

webHtmlApp is a new web build using Compose HTML instead of Compose
Multiplatform UI's Skia/canvas renderer - real <select>/<input>/<button>
elements, an anchored popup menu for reordering/removing currencies
(Compose HTML has no built-in DropdownMenu), and locale-independent
English strings (moko-resources' Compose integration pulls in
compose.foundation/ui, which this module exists to avoid).

Realizing the bundle-size win needed splitting sharedUi out of shared:
the Compose Multiplatform Gradle plugin bundles Skiko's several-MB web
runtime into any js/wasmJs target whose resolved dependencies contain
org.jetbrains.compose.ui:ui anywhere, and shared previously declared it
directly for the other (Skia-based) web app's UI. shared is now pure
business/data logic with no Compose dependency; sharedUi holds App()/
PriceScreen() for androidApp, desktopApp, and webApp to render.
PriceViewModel's ViewModel supertype and CurrencyConverter's BigDecimal
params moved from implementation() to api() in shared, since they're
part of its public surface that webHtmlApp now touches directly.

Also drops the @js-joda/timezone dependency from both web builds: the
app only ever calls TimeZone.currentSystemDefault(), which resolves to
a synthetic zone backed by the native Date offset on Kotlin/JS and
never touches the tz database - confirmed empirically on both js and
wasmJs targets. Cuts webApp's js bundle by ~950 KB and webHtmlApp's by
~800 KB.

currencyFlagEmoji() gained an explicit supportsFlagEmoji parameter
(defaulting to the existing expect/actual, false on web) so webHtmlApp
can opt in - Compose HTML renders real DOM text, so flag emoji work
fine there even though they don't on Compose Multiplatform's canvas.

website/serve-local.sh now builds and serves webHtmlApp instead of
webApp's wasmJs build, so it no longer mirrors what's actually deployed
to production; docs updated to reflect the new module layout and that
divergence, and the Pages workflow's path trigger now includes
sharedUi/** so UI changes there still redeploy the site.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

desktopApp/build.gradle.kts

@@ -7,7 +7,7 @@ plugins {
 }
 
 dependencies {
-    implementation(project(":shared"))
+    implementation(project(":sharedUi"))
 
     implementation(compose.desktop.currentOs)
     implementation(libs.kotlinx.coroutinesSwing)