codify "platform" into resolution logic, server-fn/fullstack overhaul (#4596)

overhaul dioxus fullstack using a new implementation of server_fn

This PR is a complete rewrite of dioxus fullstack designed to improve compatibility with axum and to fix a number of compilation errors based on feature flag unification plumbing through macros.

examples/04-managing-state/context_api.rs

@@ -0,0 +1,89 @@
+//! Demonstrates cross-component state sharing using Dioxus' Context API
+//!
+//! Features:
+//! - Context provider initialization
+//! - Nested component consumption
+//! - Reactive state updates
+//! - Error handling for missing context
+//! - Platform-agnostic implementation
+
+use dioxus::prelude::*;
+
+const STYLE: Asset = asset!("/examples/assets/context_api.css");
+
+fn main() {
+    launch(app);
+}
+
+#[component]
+fn app() -> Element {
+    // Provide theme context at root level
+    use_context_provider(|| Signal::new(Theme::Light));
+
+    rsx! {
+        Stylesheet { href: STYLE }
+        main {
+            class: "main-container",
+
+            h1 { "Theme Switcher" }
+            ThemeControls {}
+            ThemeDisplay {}
+        }
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Debug)]
+enum Theme {
+    Light,
+    Dark,
+}
+
+impl Theme {
+    fn stylesheet(&self) -> &'static str {
+        match self {
+            Theme::Light => "light-theme",
+            Theme::Dark => "dark-theme",
+        }
+    }
+}
+
+#[component]
+fn ThemeControls() -> Element {
+    let mut theme = use_theme_context();
+    let current_theme = *theme.read();
+    rsx! {
+        div {
+            class: "controls",
+            button {
+                class: "btn",
+                onclick: move |_| theme.set(Theme::Light),
+                disabled: current_theme== Theme::Light,
+                "Switch to Light"
+            }
+            button {
+                class: "btn",
+                onclick: move |_| theme.set(Theme::Dark),
+                disabled: current_theme == Theme::Dark,
+                "Switch to Dark"
+            }
+        }
+    }
+}
+
+#[component]
+fn ThemeDisplay() -> Element {
+    let theme = use_theme_context();
+
+    rsx! {
+        div {
+            class: "display {theme.read().stylesheet()}",
+            p { "Current theme: {theme:?}" }
+            p { "Try switching themes using the buttons above!" }
+        }
+    }
+}
+
+fn use_theme_context() -> Signal<Theme> {
+    try_use_context::<Signal<Theme>>()
+        .expect("Theme context not found. Ensure <App> is the root component.")
+}