fix: read real sample rate from SPA_PARAM_Format (like pw-top)

- Subscribe to SPA_PARAM_Format on each node via pw_node_subscribe_params
- Parse audio format with spa_format_audio_raw_parse to get actual rate/channels
- Shows real negotiated rates (48000 Hz, 44100 Hz, etc.) instead of defaults
- Added spa/param/format-utils.h, audio/format-utils.h, audio/raw-types.h

src/graph_engine.cpp

@@ -9,6 +9,9 @@
 #include <spa/pod/pod.h>
 #include <spa/pod/builder.h>
 #include <spa/pod/iter.h>
+#include <spa/param/format-utils.h>
+#include <spa/param/audio/format-utils.h>
+#include <spa/param/audio/raw-types.h>
 
 #include <cstring>
 #include <algorithm>
@@ -169,9 +172,37 @@ static void on_node_info(void *data, const struct pw_node_info *info) {
     nobj->node.ready = true;
 }
 
+// Parse audio format param (like pw-top does)
+static void on_node_param(void *data, int seq,
+    uint32_t id, uint32_t index, uint32_t next,
+    const struct spa_pod *param)
+{
+    auto *obj = static_cast<GraphEngine::Object*>(data);
+    if (!obj) return;
+    auto *nobj = static_cast<GraphEngine::NodeObj*>(obj);
+
+    if (param == NULL) return;
+    if (id != SPA_PARAM_Format) return;
+
+    uint32_t media_type, media_subtype;
+    if (spa_format_parse(param, &media_type, &media_subtype) < 0) return;
+
+    if (media_type == SPA_MEDIA_TYPE_audio && media_subtype == SPA_MEDIA_SUBTYPE_raw) {
+        struct spa_audio_info_raw info;
+        spa_zero(info);
+        if (spa_format_audio_raw_parse(param, &info) >= 0) {
+            if (info.rate > 0) nobj->node.sample_rate = info.rate;
+            if (info.channels > 0) nobj->node.channels = info.channels;
+            nobj->node.format = spa_type_audio_format_to_short_name((uint32_t)info.format);
+            nobj->node.changed = true;
+        }
+    }
+}
+
 static const struct pw_node_events node_events = {
     .version = PW_VERSION_NODE_EVENTS,
     .info = on_node_info,
+    .param = on_node_param,
 };
 
 // ============================================================================
@@ -275,6 +306,12 @@ static void create_proxy_for_object(GraphEngine::Object *obj, GraphEngine *engin
             &obj->object_listener, events, obj);
         pw_proxy_add_listener(proxy,
             &obj->proxy_listener, &proxy_events, obj);
+
+        // Subscribe to format params for nodes (like pw-top)
+        if (obj->type == GraphEngine::Object::ObjNode) {
+            uint32_t ids[1] = { SPA_PARAM_Format };
+            pw_node_subscribe_params((pw_node*)proxy, ids, 1);
+        }
     }
 }