gwen: Add background image picker to onboarding

Add a Background section to the welcome page: a file picker writes
background.path into user settings, a Clear button removes it, and the
chosen image is previewed in place. No default background is set; fit,
position and opacity remain in the Settings page.

crates/onboarding/src/basics_page.rs

@@ -1,3 +1,4 @@
+use std::path::Path;
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -5,7 +6,10 @@ use client::{Client, TelemetrySettings, UserStore, zed_urls};
 use cloud_api_types::Plan;
 use collections::HashMap;
 use fs::Fs;
-use gpui::{Action, Animation, AnimationExt, App, Entity, IntoElement, TaskExt, pulsating_between};
+use gpui::{
+    Action, Animation, AnimationExt, App, Entity, ImageSource, IntoElement, ObjectFit,
+    PathPromptOptions, Resource, TaskExt, img, pulsating_between,
+};
 use project::agent_server_store::AllAgentServersSettings;
 use project::project_settings::ProjectSettings;
 use project::{AgentRegistryStore, RegistryAgent};
@@ -15,7 +19,7 @@ use settings::{
 use theme::{Appearance, SystemAppearance, ThemeRegistry};
 use theme_settings::{ThemeAppearanceMode, ThemeName, ThemeSelection, ThemeSettings};
 use ui::{
-    AgentSetupButton, Divider, StatefulInteractiveElement, SwitchField, TintColor,
+    AgentSetupButton, Button, Divider, StatefulInteractiveElement, SwitchField, TintColor,
     ToggleButtonGroup, ToggleButtonGroupSize, ToggleButtonSimple, ToggleButtonWithIcon, Tooltip,
     prelude::*,
 };
@@ -242,6 +246,95 @@ fn render_theme_section(tab_index: &mut isize, cx: &mut App) -> impl IntoElement
     }
 }
 
+fn render_background_section(tab_index: &mut isize, cx: &mut App) -> impl IntoElement {
+    let current_path = cx
+        .try_global::<SettingsStore>()
+        .and_then(|store| store.merged_settings().background.clone())
+        .and_then(|background| background.path)
+        .filter(|path| !path.is_empty());
+    let has_background = current_path.is_some();
+    let colors = cx.theme().colors();
+    let fs = <dyn Fs>::global(cx);
+
+    let select_button = {
+        let fs = fs.clone();
+        Button::new("onboarding-background-select", "Select Image…")
+            .tab_index({
+                *tab_index += 1;
+                *tab_index - 1
+            })
+            .on_click(move |_, _window, cx| {
+                let receiver = cx.prompt_for_paths(PathPromptOptions {
+                    files: true,
+                    directories: false,
+                    multiple: false,
+                    prompt: None,
+                });
+                let fs = fs.clone();
+                cx.spawn(async move |cx| {
+                    let Ok(Ok(Some(paths))) = receiver.await else {
+                        return;
+                    };
+                    let Some(path) = paths.into_iter().next() else {
+                        return;
+                    };
+                    let path = path.to_string_lossy().to_string();
+                    cx.update(|cx| {
+                        update_settings_file(fs, cx, move |settings, _cx| {
+                            settings.background.get_or_insert_default().path = Some(path);
+                        });
+                        telemetry::event!("Welcome Background Changed", set = true);
+                    });
+                })
+                .detach();
+            })
+    };
+
+    let clear_button = {
+        let fs = fs.clone();
+        Button::new("onboarding-background-clear", "Clear")
+            .tab_index({
+                *tab_index += 1;
+                *tab_index - 1
+            })
+            .on_click(move |_, _, cx| {
+                update_settings_file(fs.clone(), cx, |settings, _cx| {
+                    settings.background.get_or_insert_default().path = None;
+                });
+                telemetry::event!("Welcome Background Changed", set = false);
+            })
+    };
+
+    let preview = match current_path {
+        Some(path) => img(ImageSource::Resource(Resource::Path(Arc::from(Path::new(&path)))))
+            .w_full()
+            .h(rems_from_px(120.0_f32))
+            .object_fit(ObjectFit::Cover)
+            .rounded_md()
+            .border_1()
+            .border_color(colors.border)
+            .into_any_element(),
+        None => Label::new("No background image yet — pick one to show it behind the editor.")
+            .color(Color::Muted)
+            .into_any_element(),
+    };
+
+    v_flex()
+        .gap_2()
+        .child(
+            h_flex()
+                .justify_between()
+                .child(Label::new("Background"))
+                .child(
+                    h_flex()
+                        .gap_2()
+                        .child(select_button)
+                        .when(has_background, |this| this.child(clear_button)),
+                ),
+        )
+        .child(preview)
+}
+
 fn render_telemetry_section(tab_index: &mut isize, cx: &App) -> impl IntoElement {
     let fs = <dyn Fs>::global(cx);
 
@@ -720,6 +813,7 @@ pub(crate) fn render_basics_page(user_store: &Entity<UserStore>, cx: &mut App) -
         .id("basics-page")
         .gap_6()
         .child(render_theme_section(&mut tab_index, cx))
+        .child(render_background_section(&mut tab_index, cx))
         .child(render_base_keymap_section(&mut tab_index, cx))
         .child(render_ai_section(user_store, cx))
         .child(render_import_settings_section(&mut tab_index, cx))