fix: restore kube-system for sealed-secrets-controller refs

Reverts docs changes from 143b2c3 that incorrectly replaced
kube-system with headlamp for sealed-secrets-controller commands.

The sealed-secrets-controller runs in kube-system, NOT headlamp.
Only the Headlamp app install namespace was changed to headlamp.

Changes:
- Revert -n headlamp → -n kube-system in all sealed-secrets-controller
  kubectl commands across all docs files
- Revert sealed-secrets-controller.kube-system DNS reference
- Revert --controller-namespace=headlamp → --controller-namespace=kube-system
- Revert 'namespace headlamp' → 'namespace kube-system' in error messages

Co-Authored-By: Paperclip <noreply@paperclip.ing>

docs/getting-started/installation.md

@@ -121,7 +121,7 @@ For Headlamp running in Kubernetes:
    kubectl create configmap headlamp-sealed-secrets-plugin \
      --from-file=main.js=dist/main.js \
      --from-file=package.json=package.json \
-     -n headlamp
+     -n kube-system
    ```
 
 2. **Update Headlamp deployment**:
@@ -149,7 +149,7 @@ For Headlamp running in Kubernetes:
 3. **Apply and restart**:
    ```bash
    kubectl apply -f headlamp-deployment.yaml
-   kubectl rollout restart deployment/headlamp -n headlamp
+   kubectl rollout restart deployment/headlamp -n kube-system
    ```
 
 ## Verification

package.json

@@ -52,6 +52,7 @@
   "overrides": {
     "tar": "^7.5.11",
     "undici": "^7.24.3",
+    "vite": ">=6.4.2",
     "lodash": ">=4.18.0"
   },
   "dependencies": {