rename render/ files to UpperCamelCase to match client convention

The render/ tree was the only place in the client still using kebab-case
filenames. Brings ~80 files in line with the rest of src/client/
(BuildPreviewController, TransformHandler, etc.). Directories kept as
they were (name-pass/, fx-pass/, passes/, utils/, debug/) since the
codebase already mixes those.

Two collisions surfaced and got resolved: render/types/ is a directory,
not a file, so its imports kept the lowercase form; and the sed pass
incidentally normalized core/pathfinding imports, which had to be
reverted since that file is actually lowercase on disk despite some
imports having referenced it as ./Types under macOS case-insensitive
resolution.

src/client/render/gl/SettingsUtils.ts

@@ -0,0 +1,49 @@
+/**
+ * Utilities for RenderSettings persistence — deep-assign, deep-diff.
+ */
+
+type Obj = Record<string, any>;
+
+/** Recursively assign source values onto target, preserving target's structure. */
+export function deepAssign(target: Obj, source: Obj): void {
+  for (const key of Object.keys(source)) {
+    if (
+      typeof source[key] === "object" &&
+      source[key] !== null &&
+      typeof target[key] === "object" &&
+      target[key] !== null
+    ) {
+      deepAssign(target[key] as Obj, source[key] as Obj);
+    } else if (key in target) {
+      target[key] = source[key];
+    }
+  }
+}
+
+/**
+ * Compute a sparse deep-partial of values that differ from defaults.
+ * Returns `undefined` if nothing differs.
+ */
+export function deepDiff(defaults: Obj, current: Obj): Obj | undefined {
+  let result: Obj | undefined;
+  for (const key of Object.keys(defaults)) {
+    const dv = defaults[key];
+    const cv = current[key];
+    if (
+      typeof dv === "object" &&
+      dv !== null &&
+      typeof cv === "object" &&
+      cv !== null
+    ) {
+      const sub = deepDiff(dv as Obj, cv as Obj);
+      if (sub !== undefined) {
+        result ??= {};
+        result[key] = sub;
+      }
+    } else if (dv !== cv) {
+      result ??= {};
+      result[key] = cv;
+    }
+  }
+  return result;
+}