ci: Atomically replace share-svc binary on deploy

scp overwrites in place, which fails with ETXTBSY ("text file busy") on
repeat deploys because systemd is executing /usr/local/bin/share-svc.
Copy to a temp path, chmod, then mv it over the destination so rename(2)
swaps the dir entry without touching the busy inode.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/deploy.yaml

@@ -64,8 +64,16 @@ jobs:
 
       - name: Copy backend binary + unit file
         run: |
+          # Copy to a temp path then atomically rename into place. You can't
+          # overwrite a running executable in place (ETXTBSY / "Text file busy"),
+          # but rename(2) just swaps the directory entry while the old inode keeps
+          # serving the running process until the restart step picks up the new
+          # binary. chmod first so the exec bit survives the rename (scp doesn't
+          # preserve mode without -p).
           scp -i ~/.ssh/deploy_key server/share-svc \
-            "$DEPLOY_USER@$DEPLOY_HOST:/usr/local/bin/share-svc"
+            "$DEPLOY_USER@$DEPLOY_HOST:/usr/local/bin/share-svc.new"
+          ssh -i ~/.ssh/deploy_key "$DEPLOY_USER@$DEPLOY_HOST" \
+            'chmod 0755 /usr/local/bin/share-svc.new && mv -f /usr/local/bin/share-svc.new /usr/local/bin/share-svc'
           scp -i ~/.ssh/deploy_key server/share-svc.service \
             "$DEPLOY_USER@$DEPLOY_HOST:/etc/systemd/system/share-svc.service"