fix(sessions): guard, gate, and test session reload

Build on the original Reload action with the fixes raised in review:

- Server reload() now refuses to run on archived (read-only) sessions
  and when the session has work in progress, mirroring archive(), so a
  reload can no longer silently abort an in-flight agent run.
- Add a sessions.reload runtime capability; the client gates both the
  reloadSession call and the Reload menu entry on it so the action only
  appears for machines whose Pi-Web runtime supports it.
- reloadSession ignores cached-new and archived sessions.
- Add server (PiSessionService + routes) and client (SessionController)
  tests covering reload success, the active-work guard, archived
  rejection, route forwarding, capability gating, and error mapping.
- Restore alphabetical parser import ordering in clients.ts.
- Add a changeset documenting the feature and the sessiond restart note.

Note: touches a session daemon code path, so pi-web-sessiond.service
must be restarted manually for the server side to take effect.

src/server/sessions/piSessionService.ts

@@ -561,8 +561,10 @@ export class PiSessionService {
   }
 
   async reload(ref: PiSessionLookup): Promise<void> {
-    const active = await this.getActive(ref);
-    await this.closeActive(active.runtime.session.sessionId);
+    await this.assertWritable(ref);
+    const session = await this.getOrOpen(ref);
+    if (this.hasActiveWork(session)) throw new Error("Stop current session activity before reloading");
+    await this.closeActive(session.sessionId);
     const reopened = await this.getActive(ref);
     this.publishStatus(reopened.runtime.session);
   }