docs(server-apps): restore .server-changes writing guidance from #4260

The .server-changes docs tidy-up from #4260 (commit 1726d57) was reverted
alongside the recovery mechanism; restoring it here since it is unrelated.

Author: nicktrn

.claude/rules/server-apps.md

@@ -14,10 +14,12 @@ area: webapp
 type: fix
 ---
 
-Brief description of what changed and why.
+Fix pages occasionally loading unstyled during deploys. The dashboard now recovers automatically.
 EOF
 ```
 
 - **area**: `webapp` | `supervisor`
 - **type**: `feature` | `fix` | `improvement` | `breaking`
 - If the PR also touches `packages/`, just the changeset is sufficient (no `.server-changes/` needed).
+
+The body ships **verbatim in user-facing release notes**. Keep it to 1–2 short sentences, non-technical, written for a dashboard user: describe what changed for them, never the implementation (no header names, endpoints, middleware, storage mechanisms, internal tools). See `.server-changes/README.md` for full guidance.