chore(build): consolidate packaging inputs and build output layout (#299)

changes/repo-root-packaging-layout.md

@@ -0,0 +1,5 @@
+type: internal
+area: build
+
+- Moved packaging inputs (electron-builder resources, Bun runtime manifests and licenses, committed release notes) under `packaging/`.
+- Build output now lands in `dist/`: packaged apps in `dist/release/`, staged Yomitan and Hachidori in `dist/yomitan/` and `dist/hachidori/`.