build: exclude electron output + local data dirs from Next file tracing

A previous packaged .app under dist-electron-builds/ carries its own
data/ tree, and output tracing tried to copy pieces of the OLD app into
the NEW standalone output during dist:mac ("Failed to copy traced
files..." warnings). Zero bytes actually leaked (the copies ENOENT'd),
but the failure mode — yesterday's build inside today's artifact — is
bad enough to fence off explicitly, same as ./repos already was.

next.config.ts

@@ -61,8 +61,15 @@ const nextConfig: NextConfig = {
   // Sibling repos checked out under ./repos/ are unrelated source trees that
   // Turbopack's NFT can otherwise rope into the trace when dynamic fs calls
   // confuse it. Keeps the build from ballooning memory tracing dead code.
+  //
+  // dist-electron-builds/ is the OUTPUT of electron-builder — a previous
+  // packaged .app sitting there contains its own data/ tree, and tracing
+  // once tried to copy pieces of the old app into the new standalone output
+  // ("Failed to copy traced files ... dist-electron-builds/..." warnings,
+  // observed 2026-08-06). Same reasoning for ./data/, a dev-run server's
+  // local state dir.
   outputFileTracingExcludes: {
-    "*": ["./repos/**/*"],
+    "*": ["./repos/**/*", "./dist-electron-builds/**/*", "./data/**/*"],
   },
   turbopack: {
     root: import.meta.dirname,