simple table is not support in dashboard

## About the bug

**Steps to reproduce:**
List the minimal actions needed to reproduce the behavior.

1. add cell
2. select simple table
3. save
4. preview dashboard is empty

**Expected behavior:**

**Actual behavior:**

**Visual Proof:**

## About your environment

**Environment info:**

**Config:**

**Logs:**

**Performance:**
Generate profiles with the following commands for bugs related to performance, locking, out of memory (OOM), etc.

```sh
# Commands should be run when the bug is actively.
# Note: This command will run for at least 30 seconds.
curl -o profiles.tar.gz "http://localhost:8086/debug/pprof/all?cpu=true"
curl -o vars.txt "http://localhost:8086/debug/vars"
iostat -xd 1 30 > iostat.txt
# Attach the `profiles.tar.gz`, `vars.txt`, and `iostat.txt` output files.
```

No file or test is named. Reproduce the issue in the dashboard by adding a cell, selecting Simple Table, saving, and previewing it; trace the Simple Table rendering path and add coverage for the empty-preview case. Done means the saved dashboard preview displays the table instead of remaining empty.

Written by the indexing model from the issue text.