Respect proxy settings when fetching JSON schemas (#53954)

This fixes #53819.

JSON schema downloads were still going through the JSON language server
without picking up Zed's configured proxy. On networks that require the
proxy, that made schema fetches fail even though the rest of the app
could connect normally.

This passes the proxy setting through to the JSON language server
configuration so schema requests follow the same network path as the
rest of Zed.

## Test plan
- `rustfmt --edition 2024 crates/languages/src/json.rs`
- `git diff --check -- crates/languages/src/json.rs`

Release Notes:

- Fixed JSON schema downloads ignoring Zed's proxy setting.

---------

Co-authored-by: Christopher Biscardi <chris@christopherbiscardi.com>

crates/languages/src/json.rs

@@ -296,6 +296,13 @@ impl LspAdapter for JsonLspAdapter {
                 }
             })
         });
+
+        if let Some(proxy_settings) = cx.update(|cx| {
+            json_schema_proxy_settings(cx.http_client().proxy().map(ToString::to_string))
+        }) {
+            merge_json_value_into(proxy_settings, &mut config);
+        }
+
         let project_options = cx.update(|cx| {
             language_server_settings(delegate.as_ref(), &self.name(), cx)
                 .and_then(|s| worktree_root(delegate, s.settings.clone()))
@@ -356,6 +363,16 @@ fn worktree_root(delegate: &Arc<dyn LspAdapterDelegate>, settings: Option<Value>
     Some(Value::Object(settings_map))
 }
 
+fn json_schema_proxy_settings(proxy: Option<String>) -> Option<Value> {
+    proxy.map(|proxy| {
+        json!({
+            "http": {
+                "proxy": proxy,
+            }
+        })
+    })
+}
+
 async fn get_cached_server_binary(
     container_dir: PathBuf,
     node: &NodeRuntime,
@@ -376,6 +393,30 @@ async fn get_cached_server_binary(
     .log_err()
 }
 
+#[cfg(test)]
+mod tests {
+    use serde_json::json;
+
+    use super::json_schema_proxy_settings;
+
+    #[test]
+    fn test_json_schema_proxy_settings_includes_proxy() {
+        assert_eq!(
+            json_schema_proxy_settings(Some("http://proxy.example:8080".to_string())),
+            Some(json!({
+                "http": {
+                    "proxy": "http://proxy.example:8080",
+                }
+            }))
+        );
+    }
+
+    #[test]
+    fn test_json_schema_proxy_settings_ignores_missing_proxy() {
+        assert_eq!(json_schema_proxy_settings(None), None);
+    }
+}
+
 pub struct NodeVersionAdapter;
 
 impl NodeVersionAdapter {