Reorganize top-level directories with clearer naming convention

app -> app-desktop-macos, presets -> app-presets, server -> remote-server,
daw-config-reaper -> osc-config-daw, plugin-reaper-realearn -> plugin-reaper-relearn.
Updated run.py and presets.py path references accordingly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugin-reaper-relearn/api/src/util.rs

@@ -0,0 +1,15 @@
+use serde::{Deserialize, Deserializer};
+
+/// Makes sure that JSON `null` is treated the same as omitting a property.
+///
+/// Use as `#[serde(deserialize_with = "deserialize_null_default")]`.
+///
+/// See https://github.com/serde-rs/serde/issues/1098#issuecomment-760711617.
+pub fn deserialize_null_default<'de, D, T>(deserializer: D) -> Result<T, D::Error>
+where
+    T: Default + Deserialize<'de>,
+    D: Deserializer<'de>,
+{
+    let opt = Option::deserialize(deserializer)?;
+    Ok(opt.unwrap_or_default())
+}