chore(release): 0.15.0 (#309)

- bump version: package.json / dsh.plugin.json / SIDEBAR_SERVICE_VERSION
- README / README_EN: consolidate the two unreleased v0.14.1 sections into
  v0.15.0 covering everything since v0.14.0 (side chat beta, file-window
  upload, desktop-compat four options, settings-page modernization,
  recommended-plugin catalog additions, subagent live batch route, drag and
  push fixes, DSH 0.1.1-rc adaptation, upload hardening); restore the
  historical v0.14.0 section; fix the glued '### v0.13.1### v0.13.1'
  heading in README_EN

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dsh-better-sidebar",
-  "version": "0.14.2",
+  "version": "0.15.0",
   "description": "DSH web plugin: a VSCode-like right sidebar (explorer / editor / terminal / git / browser), isolated per conversation session. Exposes a service for other plugins to register sidebar tabs and file viewers.",
   "type": "module",
   "repository": {