add http-json, rss, and media data source adapters

http-json: generic HTTP+JSON polling adapter, converts serde_json to domain Value. 4 tests.
rss: XML RSS feed parser, extracts items into Value array. 1 test.
media: Navidrome/Subsonic getNowPlaying adapter. 2 tests with fake server.

crates/adapters/http-json/src/lib.rs

@@ -0,0 +1,68 @@
+use domain::{DataSource, DataSourcePort, Value};
+
+pub struct HttpJsonAdapter {
+    client: reqwest::Client,
+}
+
+#[derive(Debug)]
+pub enum HttpJsonError {
+    Request(reqwest::Error),
+    NoUrl,
+    Parse(String),
+}
+
+impl std::fmt::Display for HttpJsonError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            HttpJsonError::Request(e) => write!(f, "request: {e}"),
+            HttpJsonError::NoUrl => write!(f, "no url configured"),
+            HttpJsonError::Parse(e) => write!(f, "parse: {e}"),
+        }
+    }
+}
+
+impl HttpJsonAdapter {
+    pub fn new() -> Self {
+        Self {
+            client: reqwest::Client::new(),
+        }
+    }
+}
+
+fn json_to_value(json: serde_json::Value) -> Value {
+    match json {
+        serde_json::Value::Null => Value::Null,
+        serde_json::Value::Bool(b) => Value::Bool(b),
+        serde_json::Value::Number(n) => Value::Number(n.as_f64().unwrap_or(0.0)),
+        serde_json::Value::String(s) => Value::String(s),
+        serde_json::Value::Array(arr) => {
+            Value::Array(arr.into_iter().map(json_to_value).collect())
+        }
+        serde_json::Value::Object(map) => {
+            Value::Object(map.into_iter().map(|(k, v)| (k, json_to_value(v))).collect())
+        }
+    }
+}
+
+impl DataSourcePort for HttpJsonAdapter {
+    type Error = HttpJsonError;
+
+    async fn poll(&self, source: &DataSource) -> Result<Value, Self::Error> {
+        let url = source.config.url.as_ref().ok_or(HttpJsonError::NoUrl)?;
+
+        let mut req = self.client.get(url);
+
+        for (key, val) in &source.config.headers {
+            req = req.header(key, val);
+        }
+
+        if let Some(api_key) = &source.config.api_key {
+            req = req.header("Authorization", format!("Bearer {api_key}"));
+        }
+
+        let resp = req.send().await.map_err(HttpJsonError::Request)?;
+        let json: serde_json::Value = resp.json().await.map_err(HttpJsonError::Request)?;
+
+        Ok(json_to_value(json))
+    }
+}